Biaxially oriented polypropylene film

ABSTRACT

A biaxially stretched polypropylene film of the present invention has high stiffness in the film longitudinal direction and can be manufactured by a conventional longitudinal-transverse sequential biaxial stretching method, since the biaxially stretched polypropylene film comprises a polypropylene which comprises a polypropylene having controlled specific values of a melt strength (MS) and a melt flow rate (MFR) at 230° C. or consists of a polypropylene having controlled specific values of a melt strength (MS) and a melt flow rate (MFR) at 230° C. and/or a Trouton ratio of the polypropylene is controlled at a specific value, moreover, the biaxially stretched polypropylene film contains regulated longitudinal fibrils.

RELATED APPLICATION

This is a §371 of International Application No. PCT/JP02/04466, with aninternational filing date of May 8, 2002 (WO 02/092671 A1, publishedNov. 21, 2002), which is based on Japanese Patent Application No.2001-141119, filed May 11, 2001.

TECHNICAL FIELD

This disclosure relates to a biaxially stretched polypropylene filmsuitable in a variety of use including packaging and industrial use.

BACKGROUND ART

Based on the social demand for the reduction of waste and resource,there is an increasing demand for decreasing the film thickness ofmaterials, particularly the materials for packaging uses. Presently, forexample, biaxially stretched polypropylene films having a thickness of20 μm are used as the packaging materials. Most of the biaxiallystretched polypropylene films are manufactured by conventionallongitudinal-transverse sequential biaxial stretching method. Inconventional longitudinal-transverse sequential biaxial stretchingmethod, polymer is melted by an extruder, filtered, extruded from a slitdie, and wound around a metal drum to prepare a cooled and solidifiedunstretched film. The unstretched film is passed between rolls ofdifferent rotating speeds and is stretched in the longitudinaldirection. The film is then fed into a tenter, is stretched in thetransverse direction, is heat-set, cooled, and winded. This process isthe typical process for manufacturing biaxially stretched polypropylenefilms.

Compared with the above-described biaxially stretched polypropylenefilms having a thickness of 20 μm, a 25% reduction of wastes andresources can be achieved if the same performance and the sameconverting ability can be achieved with biaxially stretchedpolypropylene films having a thickness of 15 μm.

To achieve this, biaxially stretched polypropylene films must betensilized to decrease the elongation against tension applied during theconverting process. During the converting process, the tension works inthe longitudinal direction of the film. Thus, biaxially stretchedpolypropylene films must be tensilized mainly in the longitudinaldirection.

In general, the heat shrinkage of polypropylene films tends to increaseas the polypropylene films are tensilized. When the dimensionalstability of the film decreases at high temperatures, the film shrinksduring the converting process such as printing, coating, and laminating,thereby drastically decreasing the commercial value of the film.Accordingly, the heat shrinkage must be comparable to or even lower thanthat of common biaxially stretched polypropylene films.

Japanese Patent Publication of Examined Application Nos. 41-21790,45-37879, and 49-18628 disclose methods for making films tensilized inthe longitudinal directions whereby the film is re-stretched in thelongitudinal direction after it is stretched in the longitudinal andtransverse direction to increase the longitudinal strength of the film.A drawback of these films tensilized in the longitudinal direction istheir low strength in the transverse direction. To overcome thisdrawback, Japanese Unexamined Patent Application Publication No.56-51329 discloses a method whereby a polypropylene sheet havingpredetermined melting/recrystallization temperatures re-stretched in thelongitudinal direction after it has been biaxially stretched.

However, in conventional longitudinal-transverse sequential biaxialstretching method, it has been difficult to obtain films tensilized inthe longitudinal direction. In other words, in conventionallongitudinal-transverse sequential biaxial stretching method, the filmmust be kept at a certain temperature to maintain a half-melted statebecause the oriented crystals produced by longitudinal stretching isstretched by transverse stretching. Since most of the crystals becomeoriented in the transverse direction after transverse stretching, theresulting biaxially stretched polypropylene film has a markedly highstrength in the transverse direction when compared to that in thelongitudinal direction.

The microstructure, hereinafter referred to as the “fibril structure”,of a common biaxially stretched polypropylene film manufactured by aconventional longitudinal-transverse sequential biaxial stretchingmethod is observed with an atomic force microscope (AFM). A networkstructure consisting of fibrils having a diameter of approximately 20 nmand being mainly oriented in the transverse direction is observed. Thefibrils have a high strength in the length direction, but readily deformin the width direction. This fact is considered as the cause of bias ofthe film strength in the transverse direction.

Moreover, the methods described in Japanese Patent Publication ofExamined Application No. 41-21790 and Japanese Unexamined PatentApplication Publication No. 56-51329 in which re-stretching in thelongitudinal direction is performed are complex, and require highequipment costs. Moreover, the heat shrinkage is higher than that ofcommon biaxially stretched polypropylene films, which is a problem.

SUMMARY

An embodiment (first embodiment) of the biaxially stretchedpolypropylene film is a biaxially stretched polypropylene filmcomprising a polypropylene which comprises a polypropylene having a meltstrength (MS) and a melt flow rate (MFR) measured at 230° C. thatsatisfies formula (1) below:log(MS)>−0.61 log(MFR)+0.82  (1).

Another embodiment (second embodiment) of the biaxially stretchedpolypropylene film is a biaxially stretched polypropylene filmcomprising a polypropylene which consists of a polypropylene having amelt strength (MS) and a melt flow rate (MFR) that satisfies formula (2)below:log(MS)>−0.61 log(MFR)+0.52  (2).

Another embodiment (third embodiment) of the biaxially stretchedpolypropylene film is a biaxially stretched polypropylene filmcomprising a polypropylene which comprises a polypropylene having aTrouton ratio of 30 or more.

Another embodiment (fourth embodiment) of the biaxially stretchedpolypropylene film is a biaxially stretched polypropylene filmcomprising a polypropylene which consists of a polypropylene having aTrouton ratio of 16 or more.

Another embodiment (fifth embodiment) of the biaxially stretchedpolypropylene film is a biaxially stretched polypropylene film, wherein,in a 1-μm square area of a surface of the film, one side of the areabeing parallel to the longitudinal direction, at least one longitudinalfibril having a width of at least 40 nm and extending across two sidesparallel to the transverse direction is present.

The above-described biaxially stretched polypropylene films not only aretensilized in the longitudinal direction but also have low heatshrinkage and excellent film dimensional stability at high temperatures.

DETAILED DESCRIPTION

A biaxially stretched polypropylene film of a first embodimentcomprising a polypropylene which comprises a polypropylene having a meltstrength (MS) and a melt flow rate (MFR) measured at 230° C. thatsatisfies formula (1) below will now be described:log(MS)>−0.61 log(MFR)+0.82  (1).

The first embodiment is a biaxially stretched polypropylene filmcomprising a polypropylene which comprises a polypropylene having a meltstrength (MS) and a melt flow rate (MFR) measured at 230° C. thatsatisfies formula (1) below:log(MS)>−0.61 log(MFR)+0.82  (1).This kind of polypropylene is commonly referred to as “high meltstrength (MS) polypropylene (PP), and is hereinafter denoted as“HMS-PP”.

The melt strength (MS) at 230° C. is measured by the following process.Using a melt tension tester manufactured by Toyo Seiki Kogyo Co., Ltd.,the polypropylene is heated to 230° C., and the resulting moltenpolypropylene is extruded at an extrusion rate of 15 mm/min to make astrand. The tension of the strand at a take-over rate of 6.5 m/min ismeasured, and this tension is defined as the melt strength (MS). Theunit therefor is cN.

The melt flow rate (MFR) at 230° C. is measured according to JapaneseIndustrial Standards (JIS) K 6758, whereby a melt flow rate (MFR) undera load of 2.16 kg is measured. The unit therefor is g/10 min.

Because the polypropylene used for the biaxially stretched polypropylenefilm comprises the polypropylene which comprises the polypropylene thatsatisfies formula (1), a biaxially stretched polypropylene film having ahigh strength in the longitudinal direction, which has previously beendifficult to manufacture by conventional longitudinal-transversesequential biaxial stretching method, can be manufactured. In otherwords, the polypropylene that satisfies formula (1) inhibits thelongitudinally-oriented crystals from reorienting in the transversedirection during transverse stretching.

Preferable examples of methods for preparing the polypropylenesatisfying formula (1) include a method of blending a polypropylenecontaining high-molecular-weight components in a large amount, a methodof blending polymer or oligomer having a branched structure, a methoddisclosed in Japanese Unexamined Patent Application Publication No.62-121704 in which long-chain branched structures are introduced intopolypropylene molecules, and a method disclosed in Japanese PatentPublication No. 2869606 in which a straight-chain crystallinepolypropylene having a melt strength, an intrinsic viscosity, acrystallizing temperature, and a melting point satisfy a predeterminedrelationship, and a melting point that satisfy a predeterminedrelationship, and the boiling-xylene extraction residual rate within apredetermined range is prepared without introducing long-chain branches.

The biaxially stretched polypropylene film especially preferably uses aHMS-PP, the melt strength of which is increased by introducinglong-chain branches into polypropylene molecules. Specific examples ofthe HMS-PP, the melt strength of which is increased by introducinglong-chain branches, include HMS-PP (Type name: PF-814, etc.)manufactured by Basell Polyolefins, HMS-PP (Type name: WB130HMS, etc.)manufactured by Borealis, and HMS-PP (Type name: D201, etc.)manufactured by Dow Chemical Company, etc.

An example of an index indicating the degree of long-chain branching inthe polypropylene is a branching index g represented by the equationbelow:g=[η]_(LB)/[η]_(Lin)wherein [η]_(LB) is the intrinsic viscosity of the polypropylene havinga long-chain branch, and [η]_(Lin) is the intrinsic viscosity of astraight-chain crystalline polypropylene having substantially the sameweight average molecular weight as the polypropylene having thelong-chain branch. The intrinsic viscosity is measured by a publiclyknown method in which a sample dissolved in tetralin is measured at 135°C. The weight average molecular weight is measured by a method presentedby M. L. McConnell in American Laboratory, May 63-75 (1978), i.e.,low-angle laser light scattering photometry.

The branching index g of the polypropylene which is comprised in thebiaxially stretched polypropylene film and satisfies formula (1) ispreferably 0.95 or less and more preferably, 0.9 or less. At a branchingindex exceeding 0.95, the effect of adding the polypropylene satisfyingformula (1) may be diminished, resulting in insufficient Young's modulusin the longitudinal direction when processed into a film.

The melt strength (MS) of the polypropylene, which is comprised in thebiaxially stretched polypropylene film and satisfies formula (1), ispreferably in the range of 3 to 100 cN. If a MS is less than 3 cN, theYoung's modulus in the longitudinal direction of the resulting film maybe insufficient. The Young's modulus in the longitudinal direction tendsto increase as the melt strength (MS) becomes larger. However, if a meltstrength (MS) exceeds 100 cN, film formability may be degraded. Morepreferably, the melt strength (MS) of the polypropylene satisfyingformula (1) is in the range of 4 to 80 cN, more preferably 5 to 40 cN,and most preferably 5 to 20 cN.

The content of the polypropylene satisfying the formula (1) comprised inthe biaxially stretched polypropylene film is not restricted. However,the polypropylene content is preferably 1 to 60 percent by weight. Acertain degree of effect can be achieved with a relatively smallcontent. If a polypropylene content is less than 1 percent by weight,the stretchability in the transverse direction may be degraded, andimprovements in stiffness in the longitudinal direction may be small. Ifa polypropylene content exceeds 60 percent by weight, the stretchabilityin the longitudinal direction, the impact resistance, and the haze ofthe resulting film may be degraded. More preferably, the content of thepolypropylene satisfying formula (1) is in the range of 2 to 50 percentby weight and, furthermore preferably, 3 to 40 percent by weight.

A second embodiment is a biaxially stretched polypropylene filmcomprising a polypropylene which consists of a polypropylene having amelt strength (MS) and a melt flow rate (MFR) that satisfies formula(2):log(MS)>−0.61 log(MFR)+0.52  (2).

Since the polypropylene used in the biaxially stretched polypropylenefilm comprises a polypropylene which consists of a polypropylene thatsatisfies the following formula (2), a biaxially stretched polypropylenefilm having high stiffness in the longitudinal direction, which haspreviously been difficult to manufacture by conventionallongitudinal-transverse sequential biaxial stretching method, can bemanufactured.

The polypropylene preferably satisfies formula (3) and, more preferably,satisfies formula (4). Such polypropylenes can be made by adjusting theHMS-PP content, for example. The stiffness in the longitudinal directioncan be further improved:log (MS)>−0.61 log (MFR)+0.56  (3),log (MS)>−0.61 log (MFR)+0.62  (4).

For example, the polypropylene satisfying formula (2) above can beprepared by blending a high-melt-strength polypropylene (HMS-PP) with acommon polypropylene, and by introducing long-chain branch componentsinto main-chain of the common polypropylene by means of copolymerizationor graft polymerization, so as to increase the melt strength (MS) of thepolypropylene. By blending the HMS-PP, the longitudinally orientedcrystals are prevented from being re-oriented in the transversedirection during transverse stretching.

In the first and second embodiments, the melt flow rate (MFR) of thepolypropylene used in the biaxially stretched polypropylene film ispreferably in the range of 1 to 30 g/10 min from the point of view ofthe film formability. At a melt flow rate (MFR) less than 1 g/10 min,problems such as an increase in filtration pressure during meltextrusion and an increase in time required for replacing extrusionmaterials may occur. If a melt flow rate (MFR) exceeds 30 g /10 min, thethickness irregularity in the resulting film may be large, which is aproblem. The melt flow rate (MFR) is more preferably 1 to 20 g/10 min.

In the first and second embodiments, the meso pentad fraction (mmmm) ofthe polypropylene in the biaxially stretched polypropylene film ispreferably in 90 to 99.5% and, more preferably, 94 to 99.5%. Here, themeso pentad fraction (mmmm) is the index that directly indicates theconformation of isotactic stereo-regularity in polypropylene.

Since a film having a superior dimensional stability, heat resistance,stiffness, moisture-proof property, and chemical resistance can bereliably manufactured by being the meso pentad fraction (mmmm) between90 to 99.5%, the film that exhibits high converting ability during filmconverting such as printing, coating, metallization, bag-making, andlaminating can be manufactured. If a meso pentad fraction (mmmm) is lessthan 90%, the resulting film tends to exhibit a less stiffness and alarge heat shrinkage, as the result, the converting ability duringprinting, coating, metallization, bag-making, and laminating may bedegraded, and the water vapor permeability may be increased. If a mesopentad fraction (mmmm) exceeds 99.5%, the film formability may bedegraded. More preferably, the meso pentad fraction (mmmm) is 95 to 99%,and most preferably, 96 to 98.5%.

In the first and second embodiments, the isotactic index (II) of thepolypropylene used in the biaxially stretched polypropylene film ispreferably in the range of 92 to 99.8%. If an isotactic index (II) isless than 92%, problems may arise such as less stiffness, large heatshrinkage, and degraded moisture-proof property. If an isotactic index(II) exceeds 99.8%, the film formability may be degraded. The isotacticindex (II) is more preferably in the range of 94 to 99.5%.

The polypropylene used in the biaxially stretched polypropylene film ofthe first and second embodiments may be blended with scrapped filmsproduced during manufacture of the biaxially stretched polypropylenefilm or scrapped films produced during manufacture of other types offilm or other types of resins mainly to improve economical efficiency aslong as the characteristics are not degraded.

The polypropylene used in the biaxially stretched polypropylene films ofthe first and second embodiments mainly comprises homopolymers of thepropylene. The polypropylene may be a polymer in which monomercomponents of other unsaturated hydrocarbons are copolymerized or may beblended with polymers in which propylene is copolymerized with monomercomponents other than propylene, as long as the purpose can be achieved.Examples of the copolymer components and monomer components forpreparing the blended material include ethylene, propylene (forpreparing the copolymerized blended material), 1-butene, 1-pentene,3-methylpentene-1,3-methylbutene-1,1-hexene,4-methypenten-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene,vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, and5-methyl-2-norbornene, etc.

The above-described characteristic values of the polypropylene such asthe melt strength (MS), the melt flow rate (MFR), the g value, the mesopentad fraction (mmmm), and the isotactic index (II) are preferablymeasured using raw material chips before film-formation. Alternatively,after film-formation, the film may be subjected to extraction withn-heptane at 60° C. or less for approximately 2 hours to removeimpurities and additives and then vacuum-dried at 130° C. for at least 2hours to prepare a sample. The above-described values may be measuredusing this sample.

Next, a biaxially stretched polypropylene film comprising apolypropylene which comprises a polypropylene having a Trouton ratio of30 or more is described as a third embodiment of the present invention.

The third embodiment is a biaxially stretched polypropylene filmcomprising a polypropylene which comprises a polypropylene having aTrouton ratio of 30 or more.

The Trouton ratio is measured by a converging flow method according to atheory by Cogswell [Polymer Engineering Science, 12, 64 (1972)]. TheTrouton ratio is a ratio of the extensional viscosity to shear viscosityat 230° C. and a strain rate of 60 S⁻¹ calculated from an extensionalviscosity-extensional strain rate curve and a shear viscosity-shearstrain rate curve approximated by an exponential function.

Since the biaxially stretched polypropylene film of the third embodimentcomprises a polypropylene which comprises a polypropylene having aTrouton ratio of 30 or more, a biaxially stretched polypropylene filmhaving high stiffness in the longitudinal direction, which haspreviously been difficult to manufacture by a conventionallongitudinal-transverse sequential biaxial stretching method, can bemanufactured. Namely, the polypropylene having a Trouton ratio of 30 ormore prevents the longitudinally oriented crystals from re-orienting inthe transverse direction during transverse stretching.

The Trouton ratio of the polypropylene comprised in the biaxiallystretched polypropylene film is preferably high. However, at anexcessively high ratio, the film formability and surface haze may bedegraded. The Trouton ratio of the polypropylene comprised in thebiaxially stretched polypropylene film of the present invention is morepreferably 35 or more, and furthermore preferably in the range of 40 to100.

Preferable examples of methods for preparing a polypropylene having aTrouton ratio of 30 or more include a method of blending a polypropylenecontaining high-molecular-weight components in a large amount, a methodof blending polymer or oligomer having a branched structure, a methoddisclosed in Japanese Unexamined Patent Application Publication No.62-121704 in which long-chain branched structures are introduced intopolypropylene molecules, and a method disclosed in Japanese PatentPublication No. 2869606 in which a straight-chain crystallinepolypropylene having a melt strength, an intrinsic viscosity, acrystallizing temperature, and a melting point that satisfy apredetermined relationship, and the boiling-xylene extraction residualrate within a predetermined range is prepared without introducing oflong-chain branches, which are the methods of increasing the meltstrength (MS) of the polypropylene.

Among these high melt strength polypropylene (HMS-PP) described above,the biaxially stretched polypropylene film of the third embodimentpreferably comprises a HMS-PP which has the increased melt strength byintroducing long-chain branches into polypropylene molecules. Specificexamples of the HMS-PP which has the increased melt strength byintroducing a long-chain branch include HMS-PP (Type name: PF-814, etc.)manufactured by Basell Polyolefins, HMS-PP (Type name: WB130HMS, etc.)manufactured by Borealis, and HMS-PP (Type name: D201, etc.)manufactured by Dow Chemical Company, etc.

An example of an index indicating the degree of long-chain branching inthe polypropylene is a branching index g represented by the equationbelow:g=[η]_(LB)/[η]_(Lin)wherein [η]_(LB) is the intrinsic viscosity of the polypropylene havinga long-chain branch, and [η]_(Lin) is the intrinsic viscosity of astraight-chain crystalline polypropylene having substantially the sameweight average molecular weight as the polypropylene having thelong-chain branch. The intrinsic viscosity is measured by a publiclyknown method in which a sample dissolved in tetralin is measured at 135°C. The weight average molecular weight is measured by a method presentedby M. L. McConnell in American Laboratory, May 63-75 (1978), i.e.,low-angle laser light scattering photometry.

The branching index g of the polypropylene which is comprised in thebiaxially stretched polypropylene film of the third embodiment and has aTrouton ratio of 30 or more is preferably 0.95 or less and, morepreferably, 0.9 or less. If a branching index exceeds 0.95, the effectof adding the HMS-PP may be diminished, resulting in insufficientYoung's modulus in the longitudinal direction when processed into afilm. More preferably, the branching index g is 0.9 or less.

The melt strength (MS) of the polypropylene which is comprised in thebiaxially stretched polypropylene film of the third embodiment and has aTrouton ratio of 30 or more is preferably in the range of 3 to 100 cN.If a melt strength (MS) is less than 3 cN, the Young's modulus in thelongitudinal direction of the resulting film may be insufficient. TheYoung's modulus in the longitudinal direction tends to increase as themelt strength (MS) becomes larger. However, at a melt strength (MS)exceeding 100 cN, film formability may be degraded. More preferably, themelt strength of HMS-PP is in the range of 4 to 80 cN, more preferably 5to 40 cN, and furthermore preferably 5 to 20 cN.

The content of the polypropylene having a Trouton ratio of 30 or morecomprised in the biaxially stretched polypropylene film of the thirdembodiment is not restricted. However, the content of the polypropylenehaving a Trouton ratio of 30 or more is preferably 1 to 60 percent byweight. A certain degree of effect can be achieved with a relativelysmall content. When the content of the polypropylene having a Troutonratio of 30 or more is less than 1 percent by weight, the stretchabilityin the transverse direction may be degraded, and improvements instiffness in the longitudinal direction may be small. When the contentof the polypropylene having a Trouton ratio of 30 or more exceeds 60percent by weight, the stretchability in the longitudinal direction, theimpact resistance, and the haze may be degraded. More preferably, thecontent of the polypropylene having a Trouton ratio of 30 or more is inthe range of 2 to 50 percent by weight and, furthermore preferably, 3 to40 percent by weight.

A fourth embodiment is a biaxially stretched polypropylene filmcomprising a polypropylene which consists of a polypropylene having aTrouton ratio of 16 or more.

Because the biaxially stretched polypropylene film according to thefourth embodiment comprises a polypropylene which consists of apolypropylene having a Trouton ratio of 16 or more, a biaxiallystretched polypropylene film having high stiffness in the longitudinaldirection, which has previously been difficult to manufacture byconventional longitudinal-transverse sequential biaxial stretching, canbe manufactured.

The Trouton ratio of the polypropylene used in the biaxially stretchedpolypropylene film is preferably high. However, at an excessively highratio, the film formability and the surface haze may be degraded. TheTrouton ratio of the polypropylene used in the biaxially stretchedpolypropylene film is more preferably 18 or more, furthermore preferablyin the range of 20 to 50, and most preferably in the range of 20 to 45.The Trouton ratio can be controlled by adjusting the amount of additiveHMS-PP as described below, and the stiffness in the longitudinaldirection can be further increased.

Examples of methods for preparing a polypropylene having a Trouton ratioof 16 or more include a method in which a high-melt-strengthpolypropylene (hereinafter, denoted as HMS-PP) having a high meltstrength (MS) described below is blended with a common polypropylene anda method in which long-chain branch components are introduced into themain chain of a common polypropylene by means of copolymerization orgraft polymerization, so as to increase the melt strength (MS) of thepolypropylene. With the HMSPP, the longitudinally-oriented crystals areprevented from re-orienting in the transverse direction during thetransverse stretching.

The types of polypropylene used in the biaxially stretched polypropylenefilm of the fourth embodiment are not restricted as long as the Troutonratio is 16 or more. For example, a polypropylene having followingproperties is preferably comprised.

The polypropylene preferably comprises a polypropylene having a Troutonratio of 30 or more so as to achieve a Trouton ratio of 16 or more.Examples of methods for preparing a polypropylene having a Trouton ratioof 30 or more include a method in which a high-melt-strengthpolypropylene (hereinafter, HMS-PP) having a high melt strength (MS) isblended with a common polypropylene and a method in which long-chainbranch components are introduced into the main chains of a commonpolypropylene by means of copolymerization or graft polymerization, soas to increase the melt strength (MS) of the polypropylene. With theHMSPP, the longitudinally-oriented crystals are prevented fromre-orienting in the transverse direction during the transversestretching.

In the third and fourth embodiments, the melt flow rate (MFR) of thepolypropylene used in the biaxially stretched polypropylene film ispreferably in the range of 1 to 30 g/10 min from the point of view ofthe film formability. If a melt flow rate (MFR) is less than 1 g/10 min,problems such as an increase in filtration pressure during meltextrusion and an increase in time required for replacing extrusionmaterials may occur. If a melt flow rate (MFR) exceeds 30 g /10 min, thethickness irregularity in the resulting film may be large, which is aproblem. The melt flow rate (MFR) is more preferably 1 to 20 g/10 min.

In the third and fourth embodiments, the meso pentad fraction (mmmm) ofthe polypropylene used in the biaxially stretched polypropylene film ispreferably in 90 to 99.5% and, more preferably, 94 to 99.5%. Here, themeso pentad fraction (mmmm) is the index that directly indicates theconformation of isotactic stereo-regularity in polypropylene. If a mesopentad fraction (mmmm) is 90 to 99.5%, a film having superiordimensional stability, heat resistance, stiffness, moisture-proofproperty, and chemical resistance can be reliably manufactured. Thus, afilm that exhibits high converting ability during film convertingprocesses such as printing, coating, metallization, bag-making, andlaminating can be manufactured. If a meso pentad fraction (mmmm) is lessthan 90%, the resulting film tends to exhibit a less stiffness and alarge heat shrinkage, which may result in degradation in convertingability during printing, coating, metallization, bag-making, andlaminating, and in an increase in high water vapor permeability. If ameso pentad fraction (mmmm) exceeds 99.5%, the film formability may bedegraded. More preferably, the meso pentad fraction (mmmm) is 95 to 99%and, most preferably, 96 to 98.5%.

In the third and fourth embodiments, the isotactic index (II) of thepolypropylene used in the biaxially stretched polypropylene film ispreferably in the range of 92 to 99.8%. If an isotactic index (II) isless than 92%, the resulting film may exhibit a less stiffness, a largeheat shrinkage, and may have a degraded moisture-proof property, whichare problems. If an isotactic index (II) exceeds 99.8%, the filmformability may be degraded. The isotactic index (II) is more preferablyin the range of 94 to 99.5%.

The polypropylene used in the biaxially stretched polypropylene film ofthe third and fourth embodiments may be blended with scrapped filmsproduced during manufacture of the biaxially stretched polypropylenefilm or scrapped films produced during manufacture of other types offilm or other types of resins to improve economical efficiency as longas the characteristics are not degraded.

The polypropylene used in the biaxially stretched polypropylene film ofthe third and fourth embodiments mainly comprises homopolymers of thepropylene. The polypropylene may be a polymer in which monomercomponents of other unsaturated hydrocarbons are copolymerized or may beblended with a polymer, which is prepared by copolymerizing a propylenewith a monomer component other than propylene, as long as the purposecan be achieved. Examples of the copolymer components and monomercomponents for preparing the blended material include ethylene,propylene (for preparing the copolymerized blended material), 1-butene,1-pentene, 3-methylpentene-1,3-methylbutene-1,1-hexene,4-methypentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene,vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, and5-methyl-2-norbornene, etc.

The above-described characteristic values of the polypropylene such asthe Trouton ratio, the melt strength (MS), the melt flow rate (MFR), theg value, the meso pentad fraction (mmmm), and the isotactic index (II)are preferably measured using raw material chips before film-formation.Alternatively, after film-formation, the film may be subjected toextraction with n-heptane at 60° C. or less for approximately 2 hours toremove impurities and additives and then vacuum-dried at 130° C. for atleast 2 hours to prepare a sample. The above-described values may bemeasured using this sample.

In order to increase the strength and improve the film formability, atleast one additive that has compatibility with the polypropylene and canprovide plasticity during stretching is comprised in the biaxiallystretched polypropylene films of the first, second, third, and fourthembodiments. Here, the additive that can provide plasticity refers to aplasticizer that enables stable stretching to a high stretching ratio.Without the additive, the purpose is not sufficiently achieved, and thefilm formability is degraded. The additive is preferably at least one ofpetroleum resin substantially containing no polar group and/or terpeneresin substantially containing no polar group from the point of view ofachieving stretching to a high stretching ratio and improving barrierproperty.

The petroleum resin substantially containing no polar group refers to apetroleum resin containing no polar groups such as hydroxyl, carboxyl,halogen, or sulfone, or modified forms thereof, etc. Specific examplesof the resin are cyclopentadiene resins made from petroleum unsaturatedhydrocarbon and resins containing higher olefin hydrocarbon as theprimary component.

Preferably, the glass transition temperature (hereinafter, sometimesreferred to as Tg) of the petroleum resin substantially containing nopolar group is 60° C. or more. If a glass transition temperature (Tg) isless than 60° C., the effect of improving the stiffness may be small.

Particularly preferably, a hydrogen-added (hereinafter, sometimesreferred to as hydrogenated) petroleum resin, whose hydrogenation rateis 90% or more and more preferably 99% or more, is used. Arepresentative example of the hydrogen-added petroleum resin is analicyclic petroleum resin such as polydicyclopentadiene having a glasstransition temperature (Tg) of 70° C. or more and a hydrogenation rateof 99% or more.

Examples of the terpene resin substantially containing no polar groupare terpene resins containing no polar group such as hydroxyl, aldehyde,ketone, carboxyl, halogen, or sulfone, or the modified forms thereof,etc., i.e., hydrocarbons represented by (C₅H₈)n and modified compoundsderived therefrom, wherein n is a natural number between 2 and 20.

The terpene resins are sometimes called terpenoids. Representativecompounds thereof include pinene, dipentene, carene, myrcene, ocimene,limonene, terpinolene, terpinene, sabinene, tricyclene, bisabolene,zingiberene, santalene, campholene, mirene, and totarene, etc. Inrelation to the biaxially stretched polypropylene film, hydrogen ispreferably added at hydrogenation rate of 90% or more, particularlypreferably, 99% or more. Among them, hydrogenated β-pinene andhydrogenated β-dipentene are particularly preferred.

The bromine number of the petroleum resin or the terpene resin ispreferably 10 or less, more preferably 5 or less, and most preferably 1or less.

The amount of the additive may be large enough to achieve theplasticizing effect. Preferably, the total amount of the petroleum resinand the terpene resin is in the range of 0.1 to 30 percent by weight.When the amount of the additive resins is less than 0.1 percent byweight, the effect of improving the stretchability and the stiffness inthe longitudinal direction may be small and the transparency may bedegraded. When an amount exceeds 30 percent by weight, thermaldimensional stability may be degraded, and the additive may bleed outonto the film surface, resulting in degradation of slipperiness. Theamount of additives or the total amount of the petroleum resin and theterpene resin is more preferably 1 to 20 percent by weight, andfurthermore preferably 2 to 15 percent by weight.

When a petroleum resin and/or a terpene resin that contain polar groupsis used as the additive, voids may readily be formed inside the film,the water vapor permeability may increase, and bleeding out ofantistatic agents or lubricants may be prevented due to their poorcompatibility with polypropylene.

Specific examples of additives that has compatibility with thepolypropylene and can provide plasticizing effect during stretchinginclude “Escorez” (type name: E5300 series, etc.) manufactured by TornexCo., “Clearon” (type name: P-125, etc.) manufactured by YasuharaChemical Co., Ltd., and “Arkon” (type name: P-125, etc.) manufactured byArakawa Chemical Industries, Ltd., etc.

The biaxially stretched polypropylene film of the first, second, third,and fourth embodiments can be made into a metallized film having a highgas barrier property by depositing a metallization layer on at least oneside of the film.

Moreover, at least one side of the biaxially stretched polypropylenefilm of the first, second, third, and fourth embodiments may be providedwith a coating layer composed of polyesterpolyurethane-based resin and ametallization layer. As a result, a metallized film having a superiorgas barrier property to that of the above-described metallized film canbe made.

In achieving high gas barrier property after metallization, the coatinglayer is preferably formed by applying a blended coating materialcontaining a water-soluble organic solvent and a water-soluble and/orwater-dispersible crosslinked polyesterpolyurethane-based resin, anddrying the applied coat.

The polyesterpolyurethane-based resin used in the coating layer includespolyesterpolyol obtained by esterifying dicarboxylic acid and a diolcomponent, and polyisocyanate. A chain extension agent may be included,if necessary.

Examples of the dicarboxylic acid component in thepolyesterpolyurethane-based resin used in the coating layer includeterephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid,adipic acid, trimethyladipic acid, sebacic acid, malonic acid,dimethylmalonic acid, succinic acid, glutaric acid, pimelic acid,2,2-dimethylglutaric acid, azelaic acid, fumaric acid, maleic acid,itaconic acid, 1,3-cyclopentane dicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, 1,4-naphthalicacid, diphenic acid, 4,4′-hydroxybenzoic acid, and 2,5-naphthalenedicarboxylic acid, etc.

Examples of the diol component in the polyesterpolyurethane-based resinused in the coating layer include aliphatic glycols such as ethyleneglycol, 1,4-butanediol, diethylene glycol, and triethylene glycol;aromatic diols such as 1,4-cyclohexane dimethanol; andpoly(oxyalkylene)glycols such as polyethylene glycol, polypropyleneglycol, and polytetramethylene glycol, etc.

The polyesterpolyurethane-based resin used in the coating layer may becopolymerized with hydroxycarboxylic acid, etc. such as p-hydroxybenzoic acid, etc. in addition to containing the dicarboxylic acidcomponent and the diol component. Moreover, although these have a linearstructure, branching polyester may be made using ester-formingcomponents of trivalent or more.

Examples of polyisocyanate include hexamethylene diisocyanate,diphenylmethane diisocyanate, tolylene diisocyanate, isophoronediisocyanate, tetramethylene diisocyanate, xylylene diisocyanate, lysinediisocyanate, an adduct of tolylene diisocyanate and trimethylolpropane,and an adduct of hexamethylene diisocyanate and trimethylolethane, etc.

Examples of the chain extension agent includependant-carboxyl-group-containing diols; glycols such as ethyleneglycol, diethylene glycol, propylene glycol, 1,4-butanediol,hexamethylene glycol, and neopentyl glycol; and diamines such asethylenediamine, propylenediamine, hexamethylenediamine,phenylenediamine, tolylenediamine, diphenyldiamine,diaminodiphenylmethane, diaminodiphenylmethane, anddiaminocyclohexylmethane, etc.

A specific example of the polyesterpolyurethane-based resin includes“Hydran” (type name: AP-40F, etc.) manufactured by Dainippon Ink andChemicals, Inc., etc.

In forming the coating layer, at least one of N-methylpyrrolidone,ethylcellosolve acetate, and dimethylformamide as water-soluble organicsolvents is preferably added to the coating material to improve thecoating-layer formability and increase the adhesion of the coating layerto the base layer. Particularly, N-methylpyrrolidone is preferred sinceit has a significant effect of improving the coating-layer formabilityand increasing the adhesion of the coating layer to the base layer.Preferably, the content of the water-soluble organic solvent is 1 to 15parts by weight, and more preferably 3 to 10 parts by weight relative to100 parts by weight of the polyesterpolyurethane-based resin from thepoint of view of flammability of the coating material and odor control.

Preferably, a crosslinking structure is introduced into thewater-dispersible polyesterpolyurethane-based resin so as to increasethe adhesion between the coating layer and the base layer. Examples ofthe method for obtaining such a coating material include methodsdisclosed in Japanese Unexamined Patent Application Publication Nos.63-15816, 63-256651, and 5-152159. At least one crosslinking agentselected from isocyanate compounds, epoxy compounds, and amine compoundsis added as the crosslinking component. These crosslinking agents formcrosslinks with the polyesterpolyurethane-based resin described aboveand thus increase the adhesion between the base layer and themetallization layer.

Examples of the isocyanate compounds used as the crosslinking agentsinclude toluene diisocyanate, xylene diisocyanate, naphthalenediisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate,etc., described above. However, it is not limited to these isocyanatecompounds.

Examples of the epoxy compounds used as the crosslinking agents includediglycidyl ether of bisphenol A and oligomers thereof, diglycidyl etherof hydrogenated bisphenol A and oligomers thereof, diglycidyl etherortho-phthalate, diglycidyl ether isophthalate, diglycidyl etherterephthalate, and diglycidyl ether adipate, etc. However, it is notlimited to these epoxy compounds.

Examples of the amine compounds used as the crosslinking agents includeamine compounds such as melamine, urine, and benzoguanamine, etc.; aminoresins obtained by addition condensation of the above-described aminocompounds with formaldehyde or C₁-C₆ alcohol; hexamethylenediamine; andtriethanolamine, etc. However, it is not limited to these aminecompounds.

An amine compound is preferably contained in the coating layer from thepoint of view of food hygiene and adhesion to the base material. Aspecific example of the amine compound used as the crosslinking agent is“Beckamine” (type name: APM, etc.) manufactured by Dainippon Ink andChemicals, Inc., etc.

The amount of the crosslinking agent selected from isocyanate compounds,epoxy compounds, and amine compounds is preferably 1 to 15 parts byweight, and more preferably 3 to 10 parts by weight relative to 100parts by weight of the mixed coating material containing thewater-soluble polyesterpolyurethane-based resin and the water-solubleorganic solvent from the point of view of improving the chemicalresistance and preventing degradation in the water-proof property. Whenthe amount of the crosslinking agent is less than 1 part by weight, theeffect of improving the adhesion may not be obtained. At an amountexceeding 15 parts by weight, the adhesion between the coating layer andthe base layer may be degraded presumably due to the unreacted remainingcrosslinking agent.

Moreover, a small amount of a crosslinking accelerator may be added tothe coating layer so that the coating layer composition described abovecan completely form crosslinks and cure within the time taken tomanufacture the film for metallization.

The crosslinking accelerator contained in the coating layer ispreferably a water-soluble acidic compound since it has a significantcrosslinking promoting effect. Examples of the crosslinking acceleratorinclude terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, trimethyladipic acid, sebacic acid,malonic acid, dimethylmalonic acid, succinic acid, glutaric acid,sulfonic acid, pimelic acid, 2,2-dimethylglutaric acid, azelaic acid,fumaric acid, maleic acid, itaconic acid, 1,3-cyclopentane dicarboxylicacid, 1,2-cyclohexane dicarboxylic acid, 1,4-cyclohexane dicarboxylicacid, 1,4-naphthalic acid, diphenic acid, 4,4′-hydroxy benzoic acid, and2,5-naphthalene dicarboxylic acid, etc.

A specific example of the crosslinking accelerator is “Catalyst” (typename: PTS, etc.) manufactured by Dainippon Ink and Chemicals, Inc., etc.

Moreover, inert particles may be added to the coating layer. Examples ofthe inert particles include inorganic fillers such as silica, alumina,calcium carbonate, barium sulfate, magnesium oxide, zinc oxide, andtitanium oxide, and organic polymer particles such ascrosslinked-polystyrene particles, crosslinked-acryl particles, andcrosslinked-silicon particles, etc. In addition to the inert particles,a wax-based lubricant and a mixture of these, etc. may be added.

The coating layer is preferably formed on at least one side of the baselayer to a thickness of 0.05 to 2 μm. When the thickness of the coatinglayer is less than 0.05 μm, the adhesion to the base layer is decreased,and coating defect may be formed, resulting in degradation of the gasbarrier property after metallization. When the thickness of the coatinglayer exceeds 2 μm, the time required for curing of the coating layerbecomes longer, and the crosslinking reaction described above may beincomplete, thereby degrading the gas barrier property. Moreover, whenthe coating layer is formed on the base layer during the film-formingprocess, the reclaimability of the film scraps to the base layer isdegraded, and numerous inner voids are formed by the resin of thecoating layer which acts as the nuclei, thereby degrading the mechanicalproperties.

The adhesive strength between the coating layer and the base layer ispreferably 0.6 N/cm or more. When the adhesive strength between thecoating layer and the base layer is less than 0.6 N/cm, the coatinglayer may peel off during converting, thereby imposing a significantlylarge limitation on the usage. The adhesive strength between the coatinglayer and the base layer is preferably 0.8 N/cm or more, and morepreferably 1.0 N/cm or more.

When a coating layer is formed on at least one side of the biaxiallystretched polypropylene film of the first, second, third, and fourthembodiments so that the film can be used as the film for metallization,the centerline average roughness (Ra) of the biaxially stretchedpolypropylene film of the first, second, third, and fourth embodimentsis preferably 0.01 to 0.5 μm from the point of view of handlingconvenience, slipperiness, and blocking prevention. More preferably, thecenterline average roughness is 0.02 to 0.2 am. When the centerlineaverage roughness (Ra) is less than 0.02 μm, the slipperiness may bedegraded, resulting in the degradation of handling convenience of thefilm. At a centerline average roughness (Ra) exceeding 0.2 μm, pinholesmay occur in an aluminum layer when a metallized film is made bysequentially depositing the coating layer and a metallization layer,thereby degrading the gas barrier property.

When a coating layer is formed on at least one side of the biaxiallystretched polypropylene film of the first, second, third, and fourthembodiments so that the film can be used as the film for metallization,the surface gloss of the biaxially stretched polypropylene film of thefirst, second, third, and fourth embodiments is preferably 135% or moreand, more preferably, 138% or more to ensure superior metallic glossafter metallization.

The coating layer is preferably formed by a process of applying acoating solution using a reverse roll coater, a gravure coater, a rodcoater, an air doctor coater, or other coating machines outside thepolypropylene film manufacturing process. More preferably, the coatingis performed in the film manufacturing process. More preferably,examples thereof include a method to apply coating solutions during thefilm manufacturing process, in which a coating solution is applied on anunstretched polypropylene film and then the film is sequentiallybiaxially stretched, and in which a coating solution is applied on auniaxially stretched polypropylene film and then the film is stretchedin the direction perpendicular to the uniaxial stretching. This methodin which a coating solution is applied on a uniaxially stretchedpolypropylene film and then stretching the film in the directionperpendicular to the uniaxial stretching is most preferred since thethickness of the coating layer can be uniform and the productionefficiency can be improved.

When the biaxially stretched polypropylene film of the first, second,third, and fourth embodiments is used as the film for metallization, thepolypropylene used in the base layer preferably contains no organiclubricants such as fatty acid amide, etc. in point of view of adhesionof the coating layer and the metallization layer. However, a smallamount of organic crosslinked particles or inorganic particles may beadded to provide slipperiness and improve the processability andwindability. Examples of the organic crosslinked particles added to thepolypropylene of the base layer at a small amount includecrosslinked-silicone particles, crosslinked-polymethylmethacrylateparticles, and crosslinked-polystyrene particles. Examples of theorganic particles include zeolite, calcium carbonate, silicon oxide, andaluminum silicate. The average size of these particles is preferably 0.5to 5 μm since the slipperiness can be increased without significantlydegrading the transparency of the film.

An antistatic for avoiding the troubles resulting from the staticelectrification of the film is preferably added to the biaxiallystretched polypropylene film of the first, second, third, and fourthembodiments except for when the film is used as the film formetallization having the above-described construction. The antistaticagent contained in the biaxially stretched polypropylene film of thefirst, second, third, and fourth embodiments is not restricted. However,examples of the antistatic agent include ethylene oxide adducts ofbetaine derivatives, quaternary amine compounds, alkyldiethanolaminefatty acid esters, glycerin fatty acid ester, gylceride stearates, etc.and mixtures of these.

A lubricant is preferably added to the biaxially stretched polypropylenefilm of the first, second, third, and fourth embodiments, morepreferably, in addition to the antistatic agent described above, exceptfor when the film is used as the film for metallization having theabove-described construction. The lubricant is added to improve themold-releasing property and the flowability during thermo-forming ofthermoplastic resins according to the wordings of Japanese IndustrialStandards, and to adjust the frictional force between a convertingmachine and the film surface and between the films themselves.

The lubricant added to the biaxially stretched polypropylene film of thefirst, second, third, and fourth embodiments is not restricted. However,examples of the lubricant include amide compounds such as stearamide,erucic amide, erucamide, oleamide, etc. and mixtures of these.

The content of the antistatic agent added to the biaxially stretchedpolypropylene film of the first, second, third, and fourth embodimentsis preferably 0.3 part by weight or more, and more preferably in therange of 0.4 to 1.5 parts by weight relative to 100 parts by weight ofthe polypropylene resin used. The total content of the antistatic agentand the lubricant is more preferably 0.5 to 2.0 parts by weight from thepoint of view of antistatic property and slipperiness.

Inorganic particles and/or crosslinked organic particles for increasingthe slipperiness are preferably contained in the biaxially stretchedpolypropylene film of the first, second, third, and fourth embodiments.

The term “inorganic particles” refers to inorganic particles of metalcompounds, and the inorganic particles are not restricted. However,examples of inorganic particles include particles of zeolite, calciumcarbonate, magnesium carbonate, alumina, silica, aluminum silicate,kaolin, kaolinite, talc, clay, diatomite, montmorillonite, and titaniumoxide, etc. and mixtures of these.

The term “crosslinked organic particles” refers to particles in whichpolymer compounds are crosslinked by a crosslinking agent. Thecrosslinked organic particles contained in the biaxially stretchedpolypropylene film of the first, second, third, and fourth embodimentsare not restricted. However, examples of crosslinked organic particlesinclude crosslinked particles of polymethoxysilane-based compounds,crosslinked particles of polystyrene-based compounds, crosslinkedparticles of acrylic-based compounds, crosslinked particles ofpolyurethane-based compounds, crosslinked particles of polyester-basedcompounds, crosslinked particles of fluoric-based compounds, andmixtures of these.

The average particle size of the inorganic particles and crosslinkedorganic particles is preferably in the range of 0.5 to 6 μm. If anaverage particle size of is less than 0.5 μm, the slipperiness may bedegraded. If an average particle size exceeds 6 μm, drop-off ofparticles may occur, and the film surface may be readily damaged whenthe films come into contact with each other.

The amount of the inorganic particles and/or the crosslinked organicparticles added is preferably in the range of 0.02 to 0.5 percent byweight, and more preferably 0.05 to 0.2 percent by weight from the pointof view of blocking prevention, slipperiness, and transparency.

In addition to the above-described additives, a nucleating agent, a heatstabilizer, and an antioxidant may be added to the biaxially stretchedpolypropylene film of the first, second, third, and fourth embodiments,if necessary.

Examples of the nucleating agent include sorbitol-based,organic-metal-phosphate-ester-based, organic-metal-carboxylate-based,and rosin-based nucleating agents. The amount of the nucleating agent is0.5 percent by weight or less. As the heat stabilizer,2,6-di-tertiary-butyl-4-methylphenol (BHT) or the like may be added inan amount of 0.5 percent by weight or less. As the antioxidant,tetrakis-(methylene-(3,5-di-tertiary-butyl-4-hydroxy-hydrocinnamate))butane(Irganox 1010) or the like may be added in amount of 0.5 percent byweight or less.

A publicly known polyolefin resin is preferably laminated on at leastone side of the biaxially stretched polypropylene film of the first,second, third, and fourth embodiments for the purposes other than thosedescribed above, such as prevention of bleed-out/flying-off ofadditives, adhesion of the metallization layer, high printability,enhancement of heat sealability, enhancement of print laminationproperty, enhancement of glossy appearance, haze reduction (enhancementof transparency), enhancement of releasing property, and enhancement ofslipperiness, etc.

The thickness of the laminated polyolefin resin is preferably 0.25 μm ormore and half the total thickness of the film or less. If the thicknessis less than 0.25 μm, it is difficult to form a uniform layer due tolamination defects. When the thickness exceeds half the total thicknessof the film, the effect of the surface layer on the mechanical propertybecomes large, resulting in a decrease in Young's modulus and tensionresistance of the film. This resin laminated on the surface need notsatisfy the ranges of the present invention. Examples of the laminationmethod include co-extrusion, in-line/off-line extrusion lamination andin-line/off-line coating, etc. The method is not limited to these, andthe most suitable method should be selected as needed.

At least one film surface of the biaxially stretched polypropylene filmof the first, second, third, and fourth embodiments is preferablysubjected to corona discharge treatment so as to allow the film surfaceto have a surface wetting tension of at least 35 mN/m because theprintability, adhesion, antistatic property, and lubricant bleed-outproperty can be improved. The atmospheric gas during corona dischargetreatment is preferably air, oxygen, nitrogen, carbon dioxide gas, or anitrogen/carbon dioxide mixture gas. From the point of view ofeconomical efficiency, corona discharge treatment in air is particularlypreferred.

The Young's modulus in the longitudinal direction (Y(MD)) at 25° C. ofthe biaxially stretched polypropylene film of the first, second, third,and fourth embodiments is preferably 2.5 GPa or more. When the Y(MD) at25° C. is less than 2.5 GPa, the stiffness in the transverse directionbecomes high when compared with that in the longitudinal direction,resulting in an imbalance of stiffness and insufficient firmness of thefilm. As a result, pitch displacement may occur during printing,elongation of the film may occur during laminating, and cracks may occurif the film is subjected to coating/metallization processes. In otherwords, the film may exhibit insufficient tension resistance. The Young'smodulus in the longitudinal direction (Y(MD)) at 25° C. can becontrolled by adjusting the temperature of cooling drum for cooling andsolidifying the molten material to prepare an unstretched sheet, theconditions for the longitudinal stretching (temperature, stretchingratio, etc.), the crystallinity of the polypropylene (depending on mmmm,II, etc.), the amount of the additive for providing plasticity duringstretching, and the like. The optimum film forming conditions and rawmaterials should be selected as needed, as long as the advantages of thepresent invention are not impaired. The Young's modulus in thelongitudinal direction (Y(MD)) at 25° C. is more preferably 2.7 GPa ormore, more preferably 3.0 GPa or more, and most preferably 3.2 GPa ormore.

The Young's modulus in the longitudinal direction (Y(MD)) at 80° C. ofthe biaxially stretched polypropylene film of the first, second, third,and fourth embodiments is preferably 0.4 GPa or more. When the Y(MD) at80° C. is less than 0.4 GPa, the tension resistance during filmconverting may be insufficient. The Young's modulus in the longitudinaldirection (Y(MD)) at 80° C. can be controlled by adjusting thetemperature of cooling drum for cooling and solidifying the moltenmaterial to prepare an unstretched sheet, the conditions for thelongitudinal stretching (temperature, stretching ratio, etc.), thecrystallinity of the polypropylene (depending on mmmm, II, etc.), theamount of the additive for providing plasticity during stretching, andthe like. The optimum film forming conditions and raw materials shouldbe selected as needed, as long as the advantages of the presentinvention are not impaired. The Young's modulus in the longitudinaldirection (Y(MD)) at 80° C. is more preferably 0.5 GPa or more and,furthermore preferably, 0.6 GPa or more.

In the biaxially stretched polypropylene film of the first, second,third, and fourth embodiments, the m value at 25° C. is preferably inthe range of 0.4 to 0.7 wherein the m value in terms of a Young'smodulus in the longitudinal direction (Y(MD)) and a Young's modulus inthe transverse direction (Y(TD)) is expressed as below:m=Y(MD)/(Y(MD)+Y(TD)).Here, the m value is the ratio of the Young's modulus in thelongitudinal direction to the total of the Young's moduli in thelongitudinal and transverse directions. Accordingly, a film having an mvalue of less than 0.5 has a higher stiffness in the transversedirection than in the longitudinal direction. A film having an m valueof 0.5 has a substantially balanced stiffness between the stiffness inthe longitudinal direction and the stiffness in the transversedirection. A film having an m value of more than 0.5 has a higherstiffness in the longitudinal direction than in the transversedirection. When a film has an m value of 0.4 to 0.7, the film hasbalanced and high stiffness. When the m value at 25° C. is less than0.4, the stiffness in the longitudinal direction is significantly lowerthan that in the transverse direction, resulting in an imbalance of thestiffness. This may result in insufficient tension resistance duringfilm converting and insufficient film stiffness and is therefore notpreferred. An m value exceeding 0.7 is also not preferred since thestiffness in the transverse direction may be significantly lower thanthat in the longitudinal direction and the firmness of the resultingfilm may be insufficient.

The m value at 25° C. can be controlled by adjusting the film-formingconditions, e.g., the temperature of cooling drum for cooling andsolidifying the molten material to prepare an unstretched sheet, thetemperatures during longitudinal/transverse stretching, stretchingratio, relaxation of the film after longitudinal/transverse stretching,the crystallinity of the polypropylene (depending on mmmm, II, etc.),the amount of the additive for providing plasticity during stretching,and the like. The optimum film-forming conditions and raw materialsshould be selected as needed, as long as the advantages of the presentinvention are not impaired. The m value at 25° C. is more preferably0.42 to 0.68, more preferably 0.44 to 0.65, and most preferably 0.46 to0.62. Preferably, the m value at 80° C. is also in the range of 0.4 to0.7.

The F2 value in the longitudinal direction at 25° C. of the biaxiallystretched polypropylene film of the first, second, third, and fourthembodiments is preferably 40 MPa or more. Here, the F2 value in thelongitudinal direction is a stress applied on a sample 15 cm in thelongitudinal direction and 1 cm in the transverse direction at anelongation of 2% when the sample is stretched at an original length of50 mm and a testing speed of 300 mm/min. When the F2 value in thelongitudinal direction at 25° C. is less than 40 MPa, pitch displacementmay occur during printing, elongation of the film may occur duringlaminating, and cracks may occur if the film is subjected tocoating/metallization processes. In other words, the film may exhibitinsufficient tension resistance. The F2 value in the longitudinaldirection at 25° C. is more preferably 45 MPa or more.

The F5 value in the longitudinal direction at 25° C. of the biaxiallystretched polypropylene film of the first, second, third, and fourthembodiments is preferably 50 MPa or more. Here, the F5 value in thelongitudinal direction is a stress applied on a sample 15 cm in thelongitudinal direction and 1 cm in the transverse direction at anelongation of 5% when the sample is stretched at an original length of50 mm and a testing speed of 300 mm/min. When the F5 value in thelongitudinal direction at 25° C. is less than 50 MPa, pitch displacementmay occur during printing, elongation of the film may occur duringlaminating, and cracks may occur if the film is subjected tocoating/metallization processes. In other words, the film may exhibitinsufficient tension resistance. The F5 value in the longitudinaldirection at 25° C. is more preferably 55 MPa or more.

The heat shrinkage in the longitudinal direction at 120° C. of thebiaxially stretched polypropylene film of the first, second, third, andfourth embodiments is preferably 5% or less. When the heat shrinkage inthe longitudinal direction at 120° C. exceeds 5%, an extensive degree ofshrinking occurs when the film is heated during processes such asprinting, laminating, coating, metallization, and the like, resulting inprocess failures such as defects in the film, pitch displacement, andwrinkles. The heat shrinkage in the longitudinal direction at 120° C.can be controlled by adjusting the temperature of cooling drum forcooling and solidifying the molten material to prepare an unstretchedsheet, the conditions for the longitudinal stretching (stretchingtemperature, stretching ratio, relaxation of the film after longitudinalstretching, etc.), the crystallinity of the polypropylene (depending onmmmm, II, etc.), the amount of the additive for providing plasticityduring stretching, and the like. The optimum longitudinal-stretchingconditions and raw materials should be selected as needed, as long asthe advantages are not impaired. More preferably, the heat shrinkage inthe longitudinal direction at 120° C. is 4% or less.

In the biaxially stretched polypropylene film of the first, second,third, and fourth embodiments, the sum of the heat shrinkage in thelongitudinal direction and the heat shrinkage in the transversedirection at 120° C. is preferably 8% or less and, more preferably, 6%or less. When the sum of the heat shrinkage rates in the longitudinaland transverse directions exceeds 8%, an extensive degree of shrinkingoccurs when the film is heated during processes such as printing,laminating, coating, metallization, and the like, resulting in processfailures such as defects in the film, pitch displacement, and wrinkles.The sum of the heat shrinkages in the longitudinal and transversedirections can be controlled by adjusting the film-forming conditions,e.g., the temperature of cooling drum for cooling and solidifying themolten material to prepare an unstretched sheet, the temperatures duringlongitudinal/transverse stretching, stretching ratio, relaxation of thefilm after longitudinal/transverse stretching; the crystallinity of thepolypropylene (depending on mmmm, II, etc.); the amount of the additivefor providing plasticity during stretching; and the like. The optimumfilm-forming conditions and raw materials should be selected as needed,as long as the advantages are not impaired. More preferably, the sum ofthe heat shrinkages in the longitudinal and transverse directions at120° C. is 6% or less.

The water vapor permeability of the biaxially stretched polypropylenefilm of the first, second, third, and fourth embodiments is preferably1.5 g/m²/d/0.1 mm or less. When the water vapor permeability exceeds 1.5g/m²/d/0.1 mm, the biaxially stretched polypropylene film may exhibitpoor moisture-proof property when it is used as a packaging materialthat shields the contents from the external air. The water vaporpermeability can be controlled by adjusting the film-forming conditions,e.g., the temperature of cooling drum for cooling and solidifying themolten material to prepare an unstretched sheet, the temperatures duringlongitudinal/transverse stretching, stretching ratio; the crystallinityof the polypropylene (depending on mmmm, II, etc.); the amount of theadditive for providing plasticity during stretching; and the like. Theoptimum film-forming conditions and raw materials should be selected asneeded as long as the advantages are not impaired. More preferably, thewater vapor permeability is 1.2 g/m²/d/0.1 mm or less.

Preferably, the biaxially stretched polypropylene film of the first,second, third, and fourth embodiments includes longitudinal fibrilshaving a width of 40 nm or more and extending across two sides parallelto the transverse direction in a 1-μm square film surface, one side ofwhich is parallel to the longitudinal direction.

The term “longitudinal fibrils” refers to the fibrils oriented in thelongitudinal direction when the film surface is observed with an atomicforce microscope (AFM). The longitudinal fibrils include fibrils havingundulating shapes and branching shapes to some extent. Moreover, thelongitudinal fibrils may be tilted to a certain extent from an axis inthe longitudinal direction depending on the position of the observation.The longitudinal fibrils include those preferentially oriented in thelongitudinal direction rather than the transverse direction within ±45°with respect to the axis in the longitudinal direction.

Observation with an atomic force microscope (AFM) is performed 5 timesat different positions in a 1-μm square field view, one side of which isparallel to the longitudinal direction. A film is defined to havelongitudinal fibrils if one or more longitudinal fibrils having a widthof 40 nm or more and extending across two sides parallel to thetransverse direction are observed in all of the acquired images.Preferably, longitudinal fibrils are observed in both surfaces of thefilm. Alternatively, longitudinal fibrils in only one surface may beobserved.

Because the longitudinal fibrils described above are introduced in thefirst, second, third, and fourth embodiments, the stiffness of the filmin the longitudinal direction can be significantly increased. This isbecause the longitudinal fibrils rarely deform when stress is applied inthe longitudinal direction of the film.

The longitudinal fibrils in the biaxially stretched polypropylene filmof the first, second, third, and fourth embodiments extend across twosides parallel to the transverse direction in a 1-μm square filmsurface, one side of which is parallel to the longitudinal direction.The longitudinal fibrils preferably extend across two sides parallel tothe transverse direction in a 5-μm square film surface one side of whichis parallel to the longitudinal direction and, more preferably, acrosstwo sides parallel to the transverse direction in a 10-μm square filmsurface, one side of which is parallel to the longitudinal direction.

In the biaxially stretched polypropylene films of the first, second,third, and fourth embodiments, the Young's modulus in the longitudinaldirection can be sufficiently high and thereby a sufficient tensionresistance can be achieved if one or more longitudinal fibrils arepresent in the 1-μm square film surface, one side of which is parallelto the longitudinal direction. The number of longitudinal fibrils ismore preferably 2 or more and, furthermore, preferably 3 to 10. Here, abranching longitudinal fibril is counted as one fibril. When nolongitudinal fibrils extending across two sides parallel to thetransverse direction in the 1-μm square film surface, one side of whichis parallel to the longitudinal direction are present, the fibrilstructure may readily deform in the longitudinal direction, possiblyresulting in a decrease in stiffness of the film in the longitudinaldirection and in insufficient tension resistance of the film.

The Young's modulus of the film in the longitudinal direction tends toincrease as the number of the longitudinal fibrils described aboveincreases. However, when the number is excessively large, the surfacehaze may become high. More preferably, the number of the longitudinalfibrils in the biaxially stretched polypropylene films of the first,second, third, and fourth embodiments in a 5-μm square film surface, oneside of which is parallel to the longitudinal direction, is 1 or more,more preferably 2 or more, and furthermore preferably in the range of 3to 10.

Furthermore preferably, the number of the longitudinal fibrils in thebiaxially stretched polypropylene films of the first, second, third, andfourth embodiments in a 10-μm square film surface, one side of which isparallel to the longitudinal direction, is 1 or more, more preferably 2or more, and most preferably in the range of 3 to 10.

In the biaxially stretched polypropylene films of the first, second,third, and fourth embodiments, preferably, one or more longitudinalfibrils are present in a 1-μm square film surface, one side of which isparallel to the longitudinal direction. A sufficient number oflongitudinal fibrils are present if the above-described ranges aresatisfied. Accordingly, a film having a fibril structure, which isdifficult to deform, sufficient tension resistance, glossy surface, andsuperior gas barrier property can be obtained.

The width of the longitudinal fibrils in the biaxially stretchedpolypropylene films of the first, second, third, and fourth embodimentsis preferably 40 nm or more from the point of view of providingsufficient tension resistance by increasing the Young's modulus in thelongitudinal direction of the film. Here, the term “width of thelongitudinal fibril” refers to an average value of widths of thelongitudinal fibrils measured along three straight lines extending inthe transverse direction in an image observed with the atomic forcemicroscope (AFM). The three straight lines are drawn at regular intervalbetween two sides of the image, which is parallel to the transversedirection, so as to divide the image into four equal segments. The widthof the branching longitudinal fibrils is measured as follows. The widthof the portion of the fibril containing no branching is measured asabove. As for the branching portions, the sum of the widths of all thebranching portions measured along the straight lines parallel to thetransverse direction is calculated. When the width of the longitudinalfibrils is less than 40 nm, the longitudinal fibrils may readily deformwhen a stress is applied in the longitudinal direction of the film. As aresult, the Young's modulus in the longitudinal direction may becomeinsufficient, and the tension resistance may become poor. The Young'smodulus in the longitudinal direction of the film tends to increase asthe width of the longitudinal fibrils increases. However, when thewidths of the longitudinal fibrils are excessively large, the surfacehaze may become high. The width of the longitudinal fibrils in thebiaxially stretched polypropylene film is preferably in the range of 50to 500 nm, more preferably 55 to 200 nm, and most preferably 60 to 200nm. A film having sufficient tension resistance and excellent surfacehaze and gas barrier property can be obtained when the width of thelongitudinal fibrils in the biaxially stretched polypropylene films ofthe first, second, third, and fourth embodiments is 40 nm or more.

The fibril structure of the biaxially stretched polypropylene filmpreferably includes a fine network of fibrils, having a width of about20 nm, growing from the above-described longitudinal fibrils. With sucha structure, the film can be highly firm.

Publicly known methods may be employed in manufacturing the biaxiallystretched polypropylene films of the first, second, third, and fourthembodiments. For example, a polypropylene which comprises apolypropylene satisfying formula (1) described above,log(MS)>−0.61 log(MFR)+0.82  (1)or a polypropylene which consists of a polypropylene satisfying formula(2) described above,log(MS)>−0.61 log(MFR)+0.52  (2)or a polypropylene which comprises a polypropylene having a Troutonratio of 30 or more, or a polypropylene which consists of apolypropylene having a Trouton ratio of 16 or more is blended with atleast one of petroleum resins substantially containing no polar-groupand/or terpene resins substantially containing no polar-group, and themixture is fed into an extruder. The mixture is melted at a temperatureof 200 to 290° C., filtered, and extruded from a slit die. The extrudedmixture is then wound around a cooling drum to be cooled and solidifiedinto a sheet so as to make an unstretched film. The temperature of thecooling drum is preferably 20 to 100° C. so that the film can beadequately crystallized. In this manner, a large number of longitudinalfibrils having a large length can be obtained after biaxiallystretching.

Next, the resulting unstretched film is biaxially stretched by apublicly known longitudinal-transverse sequential biaxial stretchingmethod. The important factor for making a biaxially stretchedpolypropylene film highly tensilized in the longitudinal direction isthe stretching ratio in the longitudinal direction. The reallongitudinal stretching ratio in a conventional longitudinal-transversesequential biaxial stretching method for making a polypropylene film isin the range of 4.5 to 5.5, and if a longitudinal stretching ratioexceeds 6, film-forming may become unstable, and the film may breakduring transverse stretching. On the contrary, the real longitudinalstretching ratio is preferably 6 or more. If a real longitudinalstretching ratio is less than 6, sufficient longitudinal fibrils may notbe obtained, the stiffness in the longitudinal direction of the film maybe insufficient, and the firmness of the resulting film may beinsufficient in making the thinner film. The more preferable realstretching ratio in the longitudinal direction is 7 or more, and thefurthermore preferable real longitudinal stretching ratio is 8 or more.It is sometimes preferable to perform the longitudinal stretching in twoor more steps from the point of view of tensilization in thelongitudinal direction and introduction of the longitudinal fibrils. Thelongitudinal stretching temperature is an optimum temperature selectedfrom the point of view of stability in film-forming, tensilization inthe longitudinal direction, and introduction of the longitudinalfibrils. The longitudinal stretching temperature is preferably 120 to150° C. Moreover, during the cooling process that follows longitudinalstretching, the film is preferably relaxed in the longitudinal directionto an extent that does not further induce thickness irregularity of thefilm from the point of view of dimensional stability in the longitudinaldirection.

The real stretching ratio in the transverse direction is preferably 10or less. If a real transversal stretching ratio exceeding 10, thestiffness of the resulting film in the longitudinal direction may below, the number of longitudinal fibrils may decrease, and thefilm-forming may become unstable. The transversal stretching temperatureis an optimum temperature selected from the point of view of stabilityin film-forming, thickness irregularities, tensilization in thelongitudinal direction, and introduction of the longitudinal fibrils.The transversal stretching temperature is preferably 150 to 180° C.

After stretching in the transverse direction, the film is heat-set at150 to 180° C. while relaxing the film in the transverse direction by 1%or more, cooled, and wound to obtain the biaxially stretchedpolypropylene film of the present invention.

An example method for manufacturing a film for metallization using abiaxially stretched polypropylene film of the first, second, third, andfourth embodiments will now be described. However, this disclosure isnot limited by the manufacturing method described below.

For example, a polypropylene which comprises a polypropylene satisfyingformula (1) described above,log(MS)>−0.61 log(MFR)+0.82  (1)or a polypropylene which consists of a polypropylene satisfying formula(2) described above,log(MS)>−0.61 log(MFR)+0.52  (2)or a polypropylene which comprises a polypropylene having a Troutonratio of 30 or more, or a polypropylene which consists of apolypropylene having a Trouton ratio of 16 or more is blended with atleast one of petroleum resins substantially containing no polar-groupand/or terpene resins substantially containing no polar-group. The mixedresin and/or the third layer resin are prepared. These resins are fedinto separate extruders, melted at 200 to 290° C., and are filtered. Theresins are put together inside a short pipe or a die, extruded from aslit die to form a laminate each layer of which has a target thickness,and wound around a cooling drum so as to be cooled and solidified into asheet so as to make an unstretched laminate film. The temperature of thecooling drum is preferably 20 to 100° C. so that the film can beadequately crystallized. In this manner, a large number of longitudinalfibrils having a large length can be obtained after biaxiallystretching.

The unstretched laminate film is heated to a temperature of 120 to 150°C. and stretched in the longitudinal direction to 6 times the initiallength or more. The film is then fed into a tenter-type drawing machineso as to stretch the film in the transverse direction to 10 times theinitial length or less at 150 to 180° C., relaxed by heating at 150 to180° C., and cooled. If necessary, a surface of the base layer on whicha metallization layer is to be deposited and/or the third surfaceopposite of the base layer is subjected to corona discharge treatment inair, nitrogen, or mixture gas of carbon dioxide and nitrogen. When aheat-seal layer is to be laminated as a third layer, corona dischargetreatment is preferably avoided to achieve high adhesive strength. Next,the film is wound to obtain a biaxially stretched polypropylene film formetallization.

To make a film having a superior gas barrier property, theabove-described unstretched laminate film is heated to a temperature of120 to 150° C., stretched in the longitudinal direction to 6 times theinitial length or more, and cooled. Subsequently, the above-describedcoating material is applied on the uniaxially stretched film base layer.The base layer surface may be subjected to corona discharge treatment,if necessary. The film is then fed into a tenter-type drawing machine,stretched at a temperature of 150 to 180° C. in the transverse directionto 10 times the initial length or less, relaxed by heating at 150 to180° C., and cooled. The resulting coating layer on the base layerand/or the third layer surface opposite of the base layer may besubjected to corona discharge treatment in air, nitrogen, or mixture gasof carbon dioxide and nitrogen if necessary. At this stage, when aheat-seal layer is to be laminated as a third layer, corona dischargetreatment is preferably avoided to achieve high adhesive strength. Next,the film is wound to obtain a biaxially stretched polypropylene film formetallization.

In the present invention, the biaxially stretched polypropylene film formetallization is preferably aged at 40 to 60° C. so as to accelerate thereaction in the coating layer. When the reaction in the coating layer isaccelerated, the adhesive strength of the coating layer to the baselayer and to the metallization layer can be increased, and gas barrierproperty of the film can be improved. Aging is preferably performed for12 hours or more, and more preferably 24 hours or more to improve thechemical resistance.

Next, the metallization is performed by vacuum metallization of metal. Ametal from evaporation source is deposited on the coating layer, whichcoats the surface of the biaxially stretched polypropylene film, to forma metallization layer.

Examples of the evaporation source include those of a resistance-heatingboat type, a radiation- or radio-frequency-heating crucible type, and anelectron beam heating type. The evaporation source is not restricted.

The metal used in the metallization is preferably a metal such as Al,Zn, Mg, Sn, Si, or the like. Alternatively, Ti, In, Cr, Ni, Cu, Pb, Fe,or the like may be used. These metals preferably have purities of 99% ormore, and more preferably 99.5% or more and are preferably processedinto grains, rods, tablets, wires, and crucibles.

Among the metals for metallization, an aluminum metallization layer ispreferably formed on at least one side of the film from the point ofview of durability of the metallization layer, production efficiency,and cost. Other metal components such as nickel, copper, gold, silver,chromium, zinc, and the like may be metallized sequentially orsimultaneously with aluminum.

The metallization layer preferably has a thickness of 10 nm or more, andmore preferably 20 nm or more to achieve high gas barrier property. Nolimit is imposed as to the upper limit of the thickness of themetallization layer; however, the thickness is preferably less than 50nm from the point of view of economical and production efficiencies.

The gloss of the metallization layer is preferably 600% or more, andmore preferably 700% or more.

Alternatively, a metallization layer composed of metal oxide may beformed so that the film may be used as a transparent gas-barrier filmfor packaging having a superior gas barrier property. The metal oxidemetallization layer is preferably a layer of a metal oxide such asincompletely oxidized aluminum, or incompletely oxidized silicon.Incompletely oxidized aluminum is particularly preferable from the pointof view of durability of the metallization layer, production efficiency,and cost. Metallization can be performed by publicly known methods. Forexample, in depositing the metallization layer composed of incompletelyoxidized aluminum, the film is allowed to run in a high-vacuum devicehaving a degree of vacuum of 10⁻⁴ Torr or less, aluminum metal isheated, melted, and evaporated, and a small amount of oxygen gas issupplied at the site of evaporation so that the aluminum can becoherently deposited on the film surface to form a metallization layerwhile being oxidized. The thickness of the metal oxide metallizationlayer is preferably in the range of 10 to 50 nm, and more preferably 10to 30 nm. The oxidation of the metal oxide metallization layer composedof incompletely oxidized metal proceeds after metallization and changesthe light transmittance of the metal oxide metallized film. The lighttransmittance is preferably in the range of 70 to 90%. A lighttransmittance of less than 70% is not preferred since the content cannotbe seen through the package when the film is made into a packaging bag.A light transmittance exceeding 90% is not preferred because the gasbarrier property tends to be poor when the film is made into a packagingbag.

The adhesive strength between the metallization layer and the coatinglayer of the metallized biaxially stretched polypropylene film andbetween the metal oxide metallization layer and the coating layer of themetallized biaxially stretched polypropylene is preferably 0.6 N/cm ormore, and more preferably 0.8 N/cm or more. When the adhesive strengthis less than the above-described range, the metallization layer may bepicked off when the metallized film is being wound into a roll and whenthe metallized film is being wound off for converting, resulting indegradation of the gas barrier properties.

The gas barrier properties of the films prepared by depositing ametallization layer of a metal and an oxide metal on the biaxiallystretched polypropylene films are preferably as follows. The water vaporpermeability is preferably 4 g/m²/d or less, and more preferably 1g/m²/d or less, and the oxygen permeability is preferably 200ml/m²/d/MPa or less, and more preferably 100 ml/m²/d/MPa for use in foodpackaging bags.

The biaxially stretched polypropylene films of the first, second, third,and fourth embodiments have an increased stiffness in the longitudinaldirection compared with conventional biaxially stretched polypropylenefilms without degrading important properties such as dimensionalstability and moisture-proof property. As a result, the film exhibitssuperior handling convenience and excellent tension resistance againstconverting tension applied during film converting such as printing,laminating, coating, metallizing, and bag-making. Moreover, the troublessuch as film cracks and print pitch displacement due to the quality ofbase films can be avoided. Furthermore, the stiffness in thelongitudinal direction and the tension resistance are higher than thoseof the conventional polypropylene films having the same thickness;hence, the same degree of converting property can be maintained with athickness smaller than that of conventional biaxially stretchedpolypropylene films. Accordingly, the biaxially stretched polypropylenefilms are suitable for packaging and Industrial use.

A fifth embodiment is a biaxially stretched polypropylene filmcharacterized by including longitudinal fibrils having a width of 40 nmor more and extending across two sides parallel to the transversedirection in a 1-μm square film surface, one side of which is parallelto the longitudinal direction.

The term “longitudinal fibrils” refers to the fibrils oriented in thelongitudinal direction when the film surface is observed with an atomicforce microscope (AFM). The longitudinal fibrils include fibrils havingundulating shapes and branching shapes to some extent. Moreover, thelongitudinal fibrils may be tilted to a certain extent from an axis inthe longitudinal direction depending on the position of the observation.The longitudinal fibrils include those preferentially oriented in thelongitudinal direction rather than the transverse direction within ±45°with respect to the axis in the longitudinal direction.

Observation with an atomic force microscope (AFM) is performed 5 timesat different positions in a 1-μm square field view, one side of which isparallel to the longitudinal direction. A film is defined to havelongitudinal fibrils if one or more longitudinal fibrils having a widthof 40 nm or more and extending across two sides parallel to thetransverse direction are observed in all of the acquired images.Preferably, longitudinal fibrils are observed in both surfaces of thefilm. Alternatively, longitudinal fibrils in only one surface may beobserved.

Because the longitudinal fibrils described above are introduced in thefifth embodiment of the present invention, the stiffness of the film inthe longitudinal direction can be significantly increased. This isbecause the longitudinal fibrils rarely deform when stress is applied inthe longitudinal direction of the film.

The longitudinal fibrils in the biaxially stretched polypropylene filmof the fifth embodiment extend across two sides parallel to thetransverse direction in a 1-μm square film surface, one side of which isparallel to the longitudinal direction. The longitudinal fibrilspreferably extend across two sides parallel to the transverse directionin a 5-μm square film surface, one side of which is parallel to thelongitudinal direction and, more preferably, across two sides parallelto the transverse direction in a 10-μm square film surface, one side ofwhich is parallel to the longitudinal direction.

In the biaxially stretched polypropylene film of the fifth embodiment ofthe present invention, the Young's modulus can be sufficiently high andthereby a sufficient tension resistance can be achieved if one or morelongitudinal fibrils are present in the 1-μm square film surface oneside of which is parallel to the longitudinal direction. The number oflongitudinal fibrils is more preferably 2 or more, and furthermorepreferably 3 to 10. Here, a branching longitudinal fibril is counted asone fibril. When no longitudinal fibrils extending across two sidesparallel to the transverse direction in the 1-μm square film surface oneside of which is parallel to the longitudinal direction are present, thefibril structure may readily deform in the longitudinal direction,possibly resulting in a decrease in stiffness of the film in thelongitudinal direction and in insufficient tension resistance of thefilm.

The Young's modulus of the film in the longitudinal direction increasesas the number of the longitudinal fibrils increases. However, when thenumber is excessively large, the surface haze may become high. Morepreferably, the number of the longitudinal fibrils in the biaxiallystretched polypropylene film of the fifth embodiment in a 5-μm squarefilm surface, one side of which is parallel to the longitudinaldirection, is 1 or more, more preferably 2 or more, and furthermorepreferably in the range of 3 to 10.

Furthermore preferably, the number of the longitudinal fibrils in thebiaxially stretched polypropylene film of the fifth embodiment in a10-μm square film surface, one side of which is parallel to thelongitudinal direction, is 1 or more, more preferably 2 or more, andfurthermore preferably in the range of 3 to 10.

In the biaxially stretched polypropylene film of the fifth embodiment,preferably, one or more longitudinal fibrils are present in a 1-μmsquare film surface, one side of which is parallel to the longitudinaldirection. A sufficient number of longitudinal fibrils are present ifthe above-described ranges are satisfied. Accordingly, a film having thefibril structure, which is difficult to deform, sufficient tensionresistance, glossy surface, and superior gas barrier property can beobtained.

The width of the longitudinal fibrils in the biaxially stretchedpolypropylene film of the fifth embodiment is 40 nm or more from thepoint of view of providing sufficient tension resistance by increasingthe Young's modulus in the longitudinal direction of the film. Here, theterm “width of the longitudinal fibril” refers to an average value ofwidths of the longitudinal fibrils measured along three straight linesextending in the transverse direction in an image observed with theatomic force microscope (AFM). The three straight lines are drawn atregular intervals between two sides of the image, which is parallel tothe transverse direction, so as to divide the image into four equalsegments. The width of the branching longitudinal fibrils is measured asfollows. The width of the portion of the fibril containing no branchingis measured as above. As for the branching portions, the sum of thewidths of all the branching portions measured along the straight linesparallel to the transverse direction is calculated. When the width ofthe longitudinal fibrils is less than 30 nm, the longitudinal fibrilsmay readily deform when a stress is applied in the longitudinaldirection of the film. As a result, the Young's modulus in thelongitudinal direction may become insufficient, and the tensionresistance may become poor. The Young's modulus in the longitudinaldirection of the film tends to increase as the width of the longitudinalfibrils increases. However, when the widths of the longitudinal fibrilsare excessively large, the surface haze may become high. The width ofthe longitudinal fibrils in the biaxially stretched polypropylene filmof the fifth embodiment is preferably in the range of 50 to 500 nm, morepreferably 55 to 250 nm, and most preferably 60 to 200 nm. A film havingsufficient tension resistance and excellent surface haze and gas barrierproperty can be obtained when the width of the longitudinal fibrils inthe biaxially stretched polypropylene film is 40 nm or more.

The fibril structure of the biaxially stretched polypropylene film ofthe fifth embodiment preferably includes a fine network of fibrils,having a width of about 20 nm, growing from the above-describedlongitudinal fibrils. With such a structure, the film can be highlyfirm.

Preferably, the biaxially stretched polypropylene film of the fifthembodiment comprises a high-melt-strength polypropylene (HMS-PP) havinghigher melt strength (MS) than that of conventional polypropylenes.

The melt strength (MS) and the melt flow rate (MFR) of the HMS-PPdescribed above measured at 230° C. preferably satisfy the formula:log(MS)>−0.61 log(MFR)+0.82.

The melt strength (MS) at 230° C. is measured by the following process.Using a melt tension tester manufactured by Toyo Seiki Kogyo Co., Ltd.,the polypropylene is heated to 230° C., and the resulting moltenpolypropylene is extruded at an extrusion rate of 15 mm/min to prepare astrand. The tension of the strand at a take-over rate of 6.5 m/min ismeasured, and this tension is defined as the melt strength (MS). Theunit therefor is cN.

The melt flow rate (MFR) at 230° C. is measured according to JapaneseIndustrial Standards (JIS) K 6758, whereby a melt flow rate (MFR) undera load of 2.16 kg is measured. The unit therefor is g/10 min.

Preferably, the Trouton ratio of the HMS-PP described above is 30 ormore.

The Trouton ratio is measured by a converging flow method according to atheory by Cogswell [Polymer Engineering Science, 12, 64 (1972)]. TheTrouton ratio is a ratio of the extensional viscosity to shear viscosityat 230° C. and a strain rate of 60 S⁻¹ calculated from an extensionalviscosity-extensional strain rate curve and a shear viscosity-shearstrain rate curve approximated by an exponential function.

Generally, the higher the Trouton ratio of the HMS-PP described above,the more preferable. However, at an excessively high ratio, the filmformability and surface haze may be degraded. The Trouton ratio of theHMS-PP described above is preferably 35 or more, and most preferably inthe range of 40 to 100.

Because the biaxially stretched polypropylene film of the fifthembodiment comprises the above-described HMS-PP, a biaxially stretchedpolypropylene film having high stiffness in the longitudinal direction,which has previously been difficult to manufacture by a publicly knownlongitudinal-transverse sequential biaxial stretching, can bemanufactured. In other words, the HMS-PP described above prevents thelongitudinally-oriented crystals from re-orienting in the transversedirection during transverse stretching.

Preferable examples of methods for preparing the above-described HMS-PPinclude a method whereby a polypropylene containing a large amount ofhigh-molecular-weight components is blended, a method whereby polymer oroligomer having a branch structure is blended, a method disclosed inJapanese Unexamined Patent Application Publication No. 62-121704 wherebya long-chain branched structure is introduced into a polypropylenemolecule, and a method disclosed in Japanese Patent Publication No.2869606 in which a straight-chain crystalline polypropylene, which has amelt strength, a inherent viscosity, a crystallization temperature, anda melting point that satisfy a predetermined formula and exhibits aboiling-xylene extraction residual rate within a predetermined range, isprepared without introducing long-chain branches.

Among them, the biaxially stretched polypropylene film of the fifthembodiment preferably comprises a HMS-PP, the melt strength of which isincreased by introducing long-chain branches into polypropylenemolecules. Specific examples of the HMS-PP, the melt strength of whichis increased by introducing a long-chain branch, include HMS-PP (Typename: PF-814, etc.) manufactured by Basell Polyolefins, HMS-PP (Typename: WB130HMS, etc.) manufactured by Borealis, and HMS-PP (Type name:D201, etc.) manufactured by Dow Chemical Company, etc.

An example of an index indicating the degree of long-chain branching inthe polypropylene is a branching index g represented by the equationbelow:g=[η]_(LB)/[η]_(Lin)wherein [η]_(LB) is the intrinsic viscosity of the polypropylene havinga long-chain branch, and [η]_(Lin) is the intrinsic viscosity of astraight-chain crystalline polypropylene having substantially the sameweight average molecular weight as the polypropylene having thelong-chain branch. The intrinsic viscosity is measured by a publiclyknown method in which a sample dissolved in tetralin is measured at 135°C. The weight average molecular weight is measured by a method presentedby M. L. McConnell in American Laboratory, May 63-75 (1978), i.e.,low-angle laser light scattering photometry.

The branching index g of the HMS-PP comprised in the biaxially stretchedpolypropylene film of the fifth embodiment is preferably 0.95 or less,and more preferably 0.9 or less. If a branching index exceeds 0.95, theeffect of adding the HMS-PP may be diminished, resulting in insufficientYoung's modulus in the longitudinal direction when processed into afilm.

The melt strength (MS) of the HMS-PP comprised in the biaxiallystretched polypropylene film of the fifth embodiment is preferably inthe range of 3 to 100 cN. If a MS is less than 3 cN, the Young's modulusin the longitudinal direction of the resulting film may be insufficient.The Young's modulus in the longitudinal direction tends to increase asthe melt strength (MS) becomes larger. However, if a melt strength (MS)exceeds 100 cN, film formability may be degraded. More preferably, themelt strength (MS) of the HMS-PP is in the range of 4 to 80 cN, morepreferably 5 to 40 cN, and furthermore preferably 5 to 20 cN.

The content of the HMS-PP comprised in the polypropylene used in thebiaxially stretched polypropylene film of the fifth embodiment is notrestricted. However, the HMS-PP content is preferably 1 to 60 percent byweight. A certain degree of effect can be achieved with a relativelysmall content. If a HMS-PP content is less than 1 percent by weight, thestretchability in the transverse direction may be degraded, andimprovements in the stiffness in the longitudinal direction may besmall. If a HMS-PP content exceeds 60 percent by weight, thestretchability in the longitudinal direction, the impact resistance, andthe haze of the resulting film may be degraded. More preferably, theHMS-PP content is in the range of 2 to 50 percent by weight and,furthermore preferably, 3 to 40 percent by weight.

The melt strength (MS) and the melt flow rate (MFR) measured at 230° C.of the polypropylene used in the biaxially stretched polypropylene filmof the fifth embodiment preferably satisfy the formula:log(MS)>−0.61 log(MFR)+0.52.

More preferably, the polypropylene used satisfies the formula:log(MS)>−0.61 log(MFR)+0.56.Particularly preferably, the relationship formula below is satisfied:log(MS)>−0.61 log(MFR)+0.62.The melt strength and the melt flow rate can be controlled by adjustingthe amount of the HMS-PP described above. The stiffness in thelongitudinal direction can be further increased.

For example, the polypropylene satisfying the formulalog(MS)>−0.61 log(MFR)+0.52can be prepared by blending, a high-melt-strength polypropylene (HMS-PP)having a high melt strength with a conventional polypropylene, and byintroducing long-chain branch components into the main-chain of theconventional polypropylene by means of copolymerization or graftpolymerization, so as to increase the melt strength (MS) of thepolypropylene. With the HMS-PP, the longitudinally-oriented crystals areprevented from being re-oriented in the transverse direction duringtransverse stretching.

The Trouton ratio of the polypropylene used in the biaxially stretchedpolypropylene film of the fifth embodiment is preferably 16 or more.

Generally, the Trouton ratio of the polypropylene used in the biaxiallystretched polypropylene film of the fifth embodiment is preferably high.However, at an excessively high ratio, the film formability and thesurface haze may be degraded. The Trouton ratio is more preferably 18 ormore, more preferably in the range of 20 to 50, and most preferably inthe range of 20 to 45. The Trouton ratio can be controlled by adjustingthe amount of addition of HMS-PP described above, and the stiffness inthe longitudinal direction can be further increased.

Examples of methods for preparing the polypropylene having a Troutonratio of 16 or more include a method in which a HMS-PP having a Troutonratio of 30 or more is blended with a conventional polypropylene and amethod in which long-chain branch components are introduced into themain chains of a conventional polypropylene by means of copolymerizationor graft polymerization so as to increase the melt strength (MS) of thepolypropylene. With the HMSPP, the longitudinally-oriented crystals areprevented from re-orienting in the transverse direction during thetransverse stretching.

The melt flow rate (MFR) of the polypropylene used in the biaxiallystretched polypropylene film of the fifth embodiment is preferably inthe range of 1 to 30 g/10 min from the point of view of the filmformability. If a melt flow rate (MFR) is less than 1 g/10 min, problemssuch as an increase in filtration pressure during melt extrusion and anincrease in time required for replacing extrusion materials may occur.If a melt flow rate (MFR) exceeds 30 g /10 min, the thicknessirregularity in the resulting film may be large, which is a problem. Themelt flow rate (MFR) is more preferably 1 to 20 g/10 min.

The meso pentad fraction (mmmm) of the polypropylene used in thebiaxially stretched polypropylene film of the fifth embodiment ispreferably in the range of 90 to 99.5% and, more preferably, 94 to99.5%. Here, the meso pentad fraction (mmmm) is the index that directlyindicates the conformation of isotactic stereo-regularity inpolypropylene. If a meso pentad fraction (mmmm) is 90 to 99.5%, a filmhaving superior dimensional stability, heat resistance, stiffness,moisture-proof property, and chemical resistance can be reliablymanufactured. Thus, a film that exhibits high converting ability duringfilm converting processes such as printing, coating, metallizing,bag-making, and laminating can be manufactured. If a meso pentadfraction (mmmm) is less than 90%, the resulting film tends to exhibit aless stiffness and a large heat shrinkage, which may result indegradation in converting ability during film converting such asprinting, coating, metallization, bag-making, and laminating, and in anincrease in high water vapor permeability. If a meso pentad fraction(mmmm) exceeds 99.5%, the film formability may be degraded. Morepreferably, the meso pentad fraction (mmmm) is 95 to 99% and,furthermore preferably, 96 to 98.5%.

The isotactic index (II) of the polypropylene used in the biaxiallystretched polypropylene film of the fifth embodiment is preferably inthe range of 92 to 99.8%. At an isotactic index (II) of less than 92%,the resulting film may exhibit a less stiffness, a large heat shrinkage,and may have a degraded moisture-proof property, which are problems. Ifan isotactic index (II) exceeds 99.8%, the film formability may bedegraded. The isotactic index (II) is more preferably in the range of 94to 99.5%.

The polypropylene used in the biaxially stretched polypropylene film ofthe fifth embodiment may be blended with scrapped films produced duringmanufacture of the biaxially stretched polypropylene film or scrappedfilms produced during manufacture of other types of film or other typesof resins to improve economical efficiency as long as thecharacteristics are not degraded.

The polypropylene used in the biaxially stretched polypropylene filmmainly comprises homopolymers of the propylene. The polypropylene may bea polymer in which monomer components of other unsaturated hydrocarbonsare copolymerized or may be blended with polymers in which propylene iscopolymerized with monomer components other than propylene, as long asthe purpose can be achieved. Examples of the copolymer components andmonomer components for preparing the blended material include ethylene,propylene (for preparing the copolymerized blended material), 1-butene,1-pentene, 3-methylpentene-1,3-methylbutene-1,1-hexene,4-methypentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene,vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, and5-methyl-2-norbornene, etc.

The above-described characteristic values of the polypropylene such asthe melt strength (MS), the melt flow rate (MFR), the Trouton ratio, theg value, the meso pentad fraction (mmmm), and the isotactic index (II)are preferably measured using raw material chips before film-formation.Alternatively, after film-formation, the film may be subjected toextraction with n-heptane at 60° C. or less for approximately 2 hours toremove impurities and additives and then vacuum-dried at 130° C. for atleast 2 hours to prepare a sample. The above-described values may bethen measured using this sample.

In order to increase the strength and improve the film formability, atleast one additive that has compatibility with the polypropylene and canprovide plasticity during stretching is preferably contained in thebiaxially stretched polypropylene film of the fifth embodiment. Here,the additive that can provide plasticity refers to a plasticizer thatenables stable stretching to a high stretching ratio. With the additive,the purpose is not sufficiently achieved, sufficient longitudinalfibrils cannot be obtained, and the film formability is degraded. Theadditive is preferably at least one of petroleum resins substantiallycontaining no polar groups and/or terpene resins substantiallycontaining no polar groups from the point of view of achievingstretching to a high ratio and improved barrier property.

The petroleum resins substantially containing no polar group refers topetroleum resins containing no polar groups such as hydroxyl, carboxyl,halogen, or sulfone, or modified forms thereof. Specific examples of theresins are cyclopentadiene resins made from petroleum unsaturatedhydrocarbon and resins containing higher olefin hydrocarbon as theprimary component.

Preferably, the glass transition temperature (hereinafter, sometimesreferred to as Tg) of the petroleum resin substantially containing nopolar group is 60° C. or more. If a glass transition temperature (Tg) isless than 60° C., the effect of improving the stiffness may be small.

Particularly preferably, a hydrogen-added (hereinafter, sometimesreferred to as hydrogenated) petroleum resin, whose hydrogenation rateis 90% or more and more preferably 99% or more, is used. Arepresentative example of the hydrogen-added petroleum resin is analicyclic petroleum resin such as polydicyclopentadiene having a glasstransition temperature (Tg) of 70° C. or more and a hydrogenation rateof 99% or more.

Examples of the terpene resins substantially containing no polar groupare terpene resins containing no polar group such as hydroxyl, aldehyde,ketone, carboxyl, halogen, or sulfone, or the modified forms thereof,etc., i.e., hydrocarbons represented by (C₅H₈)n and modified compoundsderived therefrom, wherein n is a natural number between 2 and 20.

The terpene resins are sometimes called terpenoids. Representativecompounds thereof include pinene, dipentene, carene, myrcene, ocimene,limonene, terpinolene, terpinene, sabinene, tricyclene, bisabolene,zingiberene, santalene, campholene, mirene, and totarene, etc. Inrelation to the biaxially stretched polypropylene film, hydrogen ispreferably added at hydrogenation rate of 90% or more, particularlypreferably, 99% or more. Among them, hydrogenated β-pinene andhydrogenated β-dipentene are particularly preferred.

The bromine number of the petroleum resin or the terpene resin ispreferably 10 or less, more preferably 5 or less, and most preferably 1or less.

The amount of the additive may be large enough to achieve theplasticizing effect. Preferably, the total amount of the petroleum resinand the terpene resin is in the range of 0.1 to 30 percent by weight.When the amount of the additive resins is less than 0.1 percent byweight, the effect of improving the stretchability and the stiffness inthe longitudinal direction may become small and the transparency may bedegraded. When an amount exceeds 30 percent by weight, thermaldimensional stability may be degraded, and the additive may bleed outonto the film surface, resulting in degradation of slipperiness. Theamount of additives or the total amount of the petroleum resin and theterpene resin is more preferably 1 to 20 percent by weight, andfurthermore preferably 2 to 15 percent by weight.

When a petroleum resin and/or a terpene resin that contain polar groupsis used as the additive, voids may readily be formed inside the film,the water vapor permeability may increase, and bleeding out ofantistatic agents or lubricants may be prevented due to their poorcompatibility with polypropylene.

Specific examples of additives that are compatible with thepolypropylene and can provide plasticizing effect during stretchinginclude “Escorez” (type name: E5300 series, etc.) manufactured by TornexCo., “Clearon” (type name: P-125, etc.) manufactured by YasuharaChemical Co., Ltd., and “Arkon” (type name: P-125, etc.) manufactured byArakawa Chemical Industries, Ltd, etc.

The biaxially stretched polypropylene film of the fifth embodiment canbe made into a metallized film having a high gas barrier property bydepositing a metallization layer on at least one side of the film.

Moreover, at least one side of the biaxially stretched polypropylenefilm of the fifth embodiment may be provided with a coating layercomposed of polyesterpolyurethane-based resin and a metallization layer.As a result, a metallized film having a superior gas barrier property tothat of the above-described metallized film can be made.

In achieving high gas barrier property after metallization, the coatinglayer is preferably formed by applying a blended coating materialcontaining a water-soluble organic solvent and a water-soluble and/orwater-dispersible crosslinked polyesterpolyurethane-based resin, anddrying the applied coat.

The polyesterpolyurethane-based resin used in the coating layer includespolyester-polyol obtained by esterifying dicarboxylic acid and a diolcomponent, and polyisocyanate. A chain extension agent may be included,if necessary.

Examples of the dicarboxylic acid component in thepolyesterpolyurethane-based resin used in the coating layer includeterephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid,adipic acid, trimethyladipic acid, sebacic acid, malonic acid,dimethylmalonic acid, succinic acid, glutaric acid, pimelic acid,2,2-dimethylglutaric acid, azelaic acid, fumaric acid, maleic acid,itaconic acid, 1,3-cyclopentane dicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, 1,4-naphthalicacid, diphenic acid, 4,4′-hydroxybenzoic acid, and 2,5-naphthalenedicarboxylic acid, etc.

Examples of the diol component in the polyesterpolyurethane-based resinused in the coating layer include aliphatic glycols such as ethyleneglycol, 1,4-butanediol, diethylene glycol, and triethylene glycol;aromatic diols such as 1,4-cyclohexane dimethanol; andpoly(oxyalkylene)glycols such as polyethylene glycol, polypropyleneglycol, and polytetramethylene glycol, etc.

The polyesterpolyurethane-based resin used in the coating layer may becopolymerized with hydroxy-carboxylic acid, etc. such as p-hydroxybenzoic acid, etc. in addition to containing the dicarboxylic acidcomponent and the diol component. Moreover, although these have a linearstructure, branching polyester may be made using ester-formingcomponents of trivalent or more.

Examples of polyisocyanate include hexamethylene diisocyanate,diphenylmethane diisocyanate, tolylene diisocyanate, isophoronediisocyanate, tetramethylene diisocyanate, xylylene diisocyanate, lysinediisocyanate, an adduct of tolylene diisocyanate and trimethylolpropane,and an adduct of hexamethylene diisocyanate and trimethylolethane, etc.

Examples of the chain extension agent includependant-carboxyl-group-containing diols; glycols such as ethyleneglycol, diethylene glycol, propylene glycol, 1,4-butanediol,hexamethylene glycol, and neopentyl glycol; and diamines such asethylenediamine, propylenediamine, hexamethylenediamine,phenylenediamine, tolylenediamine, diphenyldiamine,diaminodiphenylmethane, diaminodiphenylmethane, anddiaminocyclohexylmethane, etc.

A specific example of the polyesterpolyurethane-based resin includes“Hydran” (type name: AP-40F, etc.) manufactured by Dainippon Ink andChemicals, Inc., etc.

In forming the coating layer, at least one of N-methylpyrrolidone,ethylcellosolve acetate, and dimethylformamide as water-soluble organicsolvents is preferably added to the coating material to improve thecoating-layer formability and increase the adhesion of the coating layerto the base layer. Particularly, N-methylpyrrolidone is preferred sinceit has a significant effect of improving the coating-layer formabilityand increasing the adhesion of the coating layer to the base layer.Preferably, the content of the water-soluble organic solvent is 1 to 15parts by weight, and more preferably 3 to 10 parts by weight relative to100 parts by weight of the polyesterpolyurethane-based resin from thepoint of view of flammability of the coating material and odor control.

Preferably, a crosslinking structure is introduced into thewater-dispersible polyesterpolyurethane-based resin so as to increasethe adhesion between the coating layer and the base layer. Examples ofthe method for obtaining such a coating material include methodsdisclosed in Japanese Unexamined Patent Application Publication Nos.63-15816, 63-256651, and 5-152159. At least one crosslinking agentselected from isocyanate compounds, epoxy compounds, and amine compoundsis added as the crosslinking component. These crosslinking agents formcrosslinks with the polyesterpolyurethane-based resin described aboveand thus increase the adhesion between the base layer and themetallization layer.

Examples of the isocyanate compounds used as the crosslinking agentsinclude toluene diisocyanate, xylene diisocyanate, naphthalenediisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate,etc., described above. However, it is not limited to these isocyanatecompounds.

Examples of the epoxy compounds used as the crosslinking agents includediglycidyl ether of bisphenol A and oligomers thereof, diglycidyl etherof hydrogenated bisphenol A and oligomers thereof, diglycidyl etherorthophthalate, diglycidyl ether isophthalate, diglycidyl etherterephthalate, and diglycidyl ether adipate, etc. However, it is notlimited to these epoxy compounds.

Examples of the amine compounds used as the crosslinking agents includeamine compounds such as melamine, urine, benzoguanamine, etc.; aminoresins obtained by addition condensation of the above-described aminocompounds with formaldehyde or C₁-C₆ alcohol; hexamethylenediamine; andtriethanolamine, etc. However, it is not limited to these aminecompounds.

An amine compound is preferably contained in the coating layer from thepoint of view of food hygiene and adhesion to the base material. Aspecific example of the amine compound used as the crosslinking agent is“Beckamine” (type name: APM, etc.) manufactured by Dainippon Ink andChemicals, Inc., etc.

The amount of the crosslinking agent selected from isocyanate compounds,epoxy compounds, and amine compounds is preferably 1 to 15 parts byweight, and more preferably 3 to 10 parts by weight relative to 100parts by weight of the mixed coating material of the water-solublepolyesterpolyurethane-based resin and the water-soluble organic solventfrom the point of view of improving the chemical resistance andpreventing degradation in the water-proof property. When the amount ofthe crosslinking agent is less than above-described range, the effect ofimproving the adhesion may not be obtained. At an amount exceeding 15parts by weight, the adhesion between the coating layer and the baselayer may be degraded presumably due to the unreacted remainingcrosslinking agent.

Moreover, a small amount of a crosslinking accelerator may be added tothe coating layer so that the coating layer composition described abovecan completely form crosslinks and cure within a time taken tomanufacture a film for metallization.

The crosslinking accelerator contained in the coating layer ispreferably a water-soluble acidic compound since it has a significantcrosslinking promoting effect. Examples of the crosslinking acceleratorinclude terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, trimethyladipic acid, sebacic acid,malonic acid, dimethylmalonic acid, succinic acid, glutaric acid,sulfonic acid, pimelic acid, 2,2-dimethylglutaric acid, azelaic acid,fumaric acid, maleic acid, itaconic acid, 1,3-cyclopentane dicarboxylicacid, 1,2-cyclohexane dicarboxylic acid, 1,4-cyclohexane dicarboxylicacid, 1,4-naphthalic acid, diphenic acid, 4,4′-hydroxy benzoic acid, and2,5-naphthalene dicarboxylic acid, etc.

A specific example of the crosslinking accelerator is “Catalyst” (typename: PTS, etc.) manufactured by Dainippon Ink and Chemicals, Inc., etc.

Moreover, inert particles may be added to the coating layer. Examples ofthe inert particles include inorganic fillers such as silica, alumina,calcium carbonate, barium sulfate, magnesium oxide, zinc oxide, andtitanium oxide, and organic polymer particles such ascrosslinked-polystyrene particles, crosslinked-acryl particles, andcrosslinked-silicon particles, etc. In addition to the inert particles,a wax-based lubricant and a mixture of these, etc. may be added.

The coating layer is preferably formed on at least one side of the baselayer at a thickness of 0.05 to 2 μm. When the thickness of the coatinglayer is less than 0.05 μm, the adhesion to the base layer is decreased,and coating defect may be formed, resulting in degradation of the gasbarrier property after metallization. When the thickness of the coatinglayer exceeds 2 μm, the time required for curing of the coating layerbecomes longer, and the crosslinking reaction described above may beincomplete, thereby degrading the gas barrier property. Moreover, whenthe coating layer is formed on the base layer during the film-formingprocess, the reclaimability of the film scraps to the base layer isdegraded, and numerous inner voids are formed by the resin of thecoating layer which acts as the nuclei, thereby degrading the mechanicalproperties.

The adhesive strength between the coating layer and the base layer ispreferably 0.6 N/cm or more. When the adhesive strength between thecoating layer and the base layer is less than 0.6 N/cm, the coatinglayer may peel off during converting, thereby imposing a significantlylarge limitation on the usage. The adhesive strength between the coatinglayer and the base layer is preferably 0.8 N/cm or more, and morepreferably 1.0 N/cm or more.

When a coating layer is formed on at least one side of the biaxiallystretched polypropylene film of the fifth embodiment so that the filmcan be used as the film for metallization, the centerline averageroughness (Ra) of the biaxially stretched polypropylene film of thefifth embodiment is preferably 0.01 to 0.5 μm from the point of view ofhandling convenience, slipperiness, and blocking prevention. Morepreferably, the centerline average roughness is 0.02 to 0.2 μm. When thecenterline average roughness (Ra) is less than 0.02 μm, the slipperinessmay be degraded, resulting in the degradation of handling convenience ofthe film. At a centerline average roughness (Ra) exceeding 0.2 μm,pinholes may occur in an aluminum layer when a metallized film is madeby sequentially depositing the coating layer and a metallization layer,thereby degrading the gas barrier property.

When a coating layer is formed on at least one side of the biaxiallystretched polypropylene film of the fifth embodiment so that the filmcan be used as the film for metallization, the surface gloss of thebiaxially stretched polypropylene film of the fifth embodiment ispreferably 135% or more, and more preferably 138% or more to ensuresuperior metallic gloss after metallization.

The coating layer is preferably formed by a process of applying acoating solution using a reverse roll coater, a gravure coater, a rodcoater, an air doctor coater, or other coating machines outside thepolypropylene film manufacturing process. More preferably, the coatingis performed in the film manufacturing process. More preferably,examples thereof include a method to apply coating solutions during thefilm manufacturing process, in which a coating solution is applied on anunstretched polypropylene film and then the film is sequentiallybiaxially stretched, and in which a coating solution is applied on auniaxially stretched polypropylene film and then the film is stretchedin the direction perpendicular to the uniaxial stretching. This methodin which a coating solution is applied on a uniaxially stretchedpolypropylene film and then stretching the film in the directionperpendicular to the uniaxial stretching is most preferred since thethickness of the coating layer can be uniform and the productionefficiency can be improved.

When the biaxially stretched polypropylene film of the fifth embodimentis used as the film for metallization, the polypropylene used in thebase layer preferably contains no organic lubricants such as fatty acidamide, etc. in point of view of adhesion of the coating layer and themetallization layer. However, a small amount of organic crosslinkedparticles or inorganic particles may be added to provide slipperinessand improve the processability and windability. Examples of the organiccrosslinked particles added to the polypropylene of the base layer at asmall amount include crosslinked-silicone particles,crosslinked-polymethylmethacrylate particles, andcrosslinked-polystyrene particles, etc. Examples of the inorganicparticles include zeolite, calcium carbonate, silicon oxide, andaluminum silicate, etc. The average particle size of these particles ispreferably 0.5 to 5 μm since the slipperiness can be increased withoutsignificantly degrading the transparency of the film.

An antistatic agent for avoiding the troubles resulting from the staticelectrification of the film is preferably added to the biaxiallystretched polypropylene film of the fifth embodiment except for when thefilm is used as the film for metallization having the above-describedconstruction. The antistatic agent contained in the biaxially stretchedpolypropylene film of the fifth embodiment is not restricted. However,examples of the antistatic agent include ethylene oxide adducts ofbetaine derivatives, quaternary amine compounds, alkyldiethanolaminefatty acid esters, glycerin fatty acid ester, gylceride stearates, etc.and mixtures of these.

A lubricant is preferably added, more preferably, in addition to theantistatic agent described above except for when the film is used as thefilm for metallization having the above-described construction. Thelubricant is added to improve the mould-releasing property and theflowability during thermo-forming of thermoplastic resins according tothe wordings of Japanese Industrial Standards, and to adjust thefrictional force between a converting machine and the film surface andbetween the films themselves.

The lubricant is not restricted. However, examples of the lubricantsinclude amide compounds such as stearamide, erucic amide, erucamide,oleamide, etc. and mixtures of these.

The content of the antistatic agent is preferably 0.3 parts by weight ormore, and more preferably in the range of 0.4 to 1.5 parts by weightrelative to 100 parts by weight of the polypropylene resin used. Thetotal content of the antistatic agent and the lubricant is morepreferably 0.5 to 2.0 parts by weight from the point of view ofantistatic property and slipperiness.

Inorganic particles and/or crosslinked organic particles for increasingthe slipperiness are preferably contained in the biaxially stretchedpolypropylene film of the fifth embodiment.

The term “inorganic particles” refers to inorganic particles of metalcompounds, and the inorganic particle is not restricted. However,examples of inorganic particles include inorganic particles of zeolite,calcium carbonate, magnesium carbonate, alumina, silica, aluminumsilicate, kaolin, kaolinite, talc, clay, diatomite, montmorillonite, andtitanium oxide, etc. and mixtures of these.

The term “crosslinked organic particles” refers to particles in whichpolymer compounds are crosslinked by a crosslinking agent. Thecrosslinked organic particles contained in the biaxially stretchedpolypropylene film are not restricted. However, examples of crosslinkedorganic particles include crosslinked particles ofpolymethoxysilane-based compounds, crosslinked particles ofpolystyrene-based compounds, crosslinked particles of acrylic-basedcompounds, crosslinked particles of polyurethane-based compounds,crosslinked particles of polyester-based compounds, crosslinkedparticles of fluoric-based compounds, and mixtures of these.

The average particle size of the inorganic particles and crosslinkedorganic particles is preferably in the range of 0.5 to 6 μm. If anaverage particle size of is less than 0.5 μm, the slipperiness may bedegraded. If an average particle size exceeds 6 μm, drop-off ofparticles may occur, and the film surface may be readily damaged whenthe films come into contact with each other.

The amount of the inorganic particles and/or the crosslinked organicparticles added is preferably in the range of 0.02 to 0.5 percent byweight, and more preferably 0.05 to 0.2 percent by weight from the pointof view of blocking prevention, slipperiness, and transparency.

In addition to the above-described additives, a nucleating agent, a heatstabilizer, and an antioxidant may be added to the biaxially stretchedpolypropylene film of the fifth embodiment, if necessary.

Examples of the nucleating agent include sorbitol-based,organic-metal-phosphate-ester-based, organic-metalcarboxylate-based, androsin-based nucleating agents. The amount of the nucleating agent is 0.5percent by weight or less. As the heat stabilizer,2,6-di-tertiary-butyl-4-methylphenol (BHT) or the like may be added inamount of 0.5 percent by weight or less. As the antioxidant,tetrakis-(methylene-(3,5-di-tertiary-butyl-4-hydroxy-hydrocinnamate))butane(Irganox 1010) or the like may be added in amount of 0.5 percent byweight or less.

A publicly known polyolefin resin is preferably laminated on at leastone side of the biaxially stretched polypropylene film of the fifthembodiment for the purposes other than those described above, such asprevention of bleed-out/flying-off of additives, adhesion of themetallization layer, high printability, enhancement of heat sealability,enhancement of print-lamination property, enhancement of glossyappearance, haze reduction (enhancement of transparency), enhancement ofreleasing property, and enhancement of slipperiness, etc.

The thickness of the laminated polyolefin resin is preferably 0.25 μm ormore and half the total thickness of the film or less. If a thickness isless than 0.25 μm, it is difficult to form a uniform layer due tolamination defects. When the thickness exceeds half the total thicknessof the film, the effect of the surface layer on the mechanical propertybecomes large, resulting in a decrease in Young's modulus and tensionresistance of the film. This resin laminated on the surface need notsatisfy the ranges of the present invention. Examples of the laminationmethod include co-extrusion, in-line/off-line extrusion lamination andin-line/off-line coating, etc. The method is not limited to these, andthe most suitable method should be selected as needed.

At least one film surface of the biaxially stretched polypropylene filmof the fifth embodiment is preferably subjected to corona dischargetreatment so as to allow the film surface to have a surface wettingtension of at least 35 mN/m because the printability, adhesion,antistatic property, and lubricant bleed-out property can be improved.The atmospheric gas during corona discharge treatment is preferably air,oxygen, nitrogen, carbon dioxide gas, or a nitrogen/carbon dioxidemixture gas. From the point of view of economical efficiency, coronadischarge treatment in air is particularly preferred.

The Young's modulus in the longitudinal direction (Y(MD)) at 25° C. ofthe biaxially stretched polypropylene film of the fifth embodiment ispreferably 2.5 GPa or more. When the Y(MD) at 25° C. is less than 2.5GPa, the stiffness in the transverse direction becomes high whencompared with that in the longitudinal direction, resulting in animbalance of stiffness and insufficient firmness of the film. As aresult, the film may exhibit insufficient tension resistance. TheYoung's modulus in the longitudinal direction (Y(MD)) at 25° C. can becontrolled by adjusting the temperature of cooling drum for cooling andsolidifying the molten material to prepare an unstretched sheet, theconditions for the longitudinal stretching (temperature, stretchingratio, etc.), the crystallinity of the polypropylene (depending on mesopentad fraction (mmmm), isotactic index (II), etc.), the amount of theadditive for providing plasticity during stretching, and the like. Theoptimum film forming conditions and raw materials should be selected asneeded, as long as the advantages are not impaired. The Young's modulusin the longitudinal direction (Y(MD)) at 25° C. is more preferably 2.7GPa or more, yet more preferably 3.0 GPa or more, and most preferably3.2 GPa or more.

The Young's modulus in the longitudinal direction (Y(MD)) at 80° C. ofthe biaxially stretched polypropylene film of the fifth embodiment ispreferably 0.4 GPa or more. When the Y(MD) at 80° C. is less than 0.4GPa, the tension resistance during film converting may be insufficient.The Young's modulus (Y(MD)) in the longitudinal direction at 80° C. canbe controlled by adjusting the temperature of cooling drum for coolingand solidifying the molten material to prepare an unstretched sheet, theconditions for the longitudinal stretching (temperature, stretchingratio, etc.), the crystallinity of the polypropylene (depending on mesopentad fraction (mmmm), isotactic index (II), etc.), the amount of theadditive for providing plasticity during stretching, and the like. Theoptimum film forming conditions and raw materials should be selected asneeded, as long as the advantages are not impaired. The Young's modulusin the longitudinal direction (Y(MD)) at 80° C. is more preferably 0.5GPa or more, and furthermore preferably 0.6 GPa or more.

In the biaxially stretched polypropylene film of the fifth embodiment,the m value at 25° C. is preferably in the range of 0.4 to 0.7 whereinthe m value in terms of a Young's modulus in the longitudinal direction(Y(MD)) and a Young's modulus in the transverse direction (Y(TD)) isexpressed as below:m=Y(MD)/(Y(MD)+Y(TD))Here, the m value is the ratio of the Young's modulus in thelongitudinal direction to the total of the Young's moduli in thelongitudinal and transverse directions. Accordingly, a film having an mvalue of less than 0.5 has a higher stiffness in the transversedirection than in the longitudinal direction. A film having an m valueof 0.5 has a substantially balanced stiffness between the stiffness inthe longitudinal direction and the stiffness in the transversedirection. A film having an m value of more than 0.5 has a higherstiffness in the longitudinal direction than in the transversedirection. When a film has an m value of 0.4 to 0.7, the film hasbalanced and high stiffness. When the m value at 25° C. is less than0.4, the stiffness in the longitudinal direction is significantly lowerthan that in the transverse direction, resulting in an imbalance of thestiffness. This may result in insufficient tension resistance duringfilm converting and insufficient film stiffness and is therefore notpreferred. An m value exceeding 0.7 is also not preferred since thestiffness in the transverse direction may be significantly lower thanthat in the longitudinal direction and the firmness of the resultingfilm may be insufficient.

The m value at 25° C. can be controlled by adjusting the film-formingconditions, e.g., the temperature of cooling drum for cooling andsolidifying the molten material to prepare an unstretched sheet, thetemperatures during longitudinal/transverse stretching, stretchingratio, relaxation of the film after longitudinal/transverse stretching;the crystallinity of the polypropylene (depending on meso pentadfraction (mmmm), isotactic index (II), etc.): the amount of the additivefor providing plasticity during stretching, and the like. The optimumfilm-forming conditions and raw materials should be selected as needed,as long as the advantages of the present invention are not impaired. Them value at 25° C. is more preferably 0.42 to 0.68, yet more preferably0.44 to 0.65, and most preferably 0.46 to 0.62. Preferably, the m valueat 80° C. is also in the range of 0.4 to 0.7.

The F2 value in the longitudinal direction at 25° C. of the biaxiallystretched polypropylene film of the fifth embodiment of the presentinvention is preferably 40 MPa or more. Here, the F2 value in thelongitudinal direction is a stress applied on a sample 15 cm in thelongitudinal direction and 1 cm in the transverse direction at anelongation of 2% when the sample is stretched at an original length of50 mm and a testing speed of 300 mm/min. When the F2 value in thelongitudinal direction at 25° C. is less than 40 MPa, the stiffness inthe transverse direction becomes higher than that in the longitudinaldirection, resulting in a film having an imbalanced stiffness and lowfirmness. Moreover, the tension resistance of the film may be poor. TheF2 value is more preferably 45 MPa in the longitudinal direction at 25°C. or more.

The F5 value in the longitudinal direction at 25° C. of the biaxiallystretched polypropylene film of the fifth embodiment is preferably 50MPa or more. Here, the F5 value in the longitudinal direction is astress applied on a sample 15 cm in the longitudinal direction and 1 cmin the transverse direction at an elongation of 5% when the sample isstretched at an original length of 50 mm and a testing speed of 300mm/min. When the F5 value in the longitudinal direction at 25° C. isless than 50 MPa, the stiffness in the transverse direction becomeshigher than that in the longitudinal direction, resulting in a filmhaving an imbalanced stiffness and low firmness. Moreover, the tensionresistance of the film may be poor. The F5 value in the longitudinaldirection at 25° C. is more preferably 55 MPa or more.

The heat shrinkage in the longitudinal direction (S(MD)) at 120° C. ofthe biaxially stretched polypropylene film of the fifth embodiment ispreferably 5% or less. When the heat shrinkage in the longitudinaldirection at 120° C. exceeds 5%, an extensive degree of shrinking occurswhen the film is heated during processes such as printing, laminating,coating, metallizing, and the like, resulting in process failures suchas defects in the film, pitch displacement, and wrinkles. The heatshrinkage in the longitudinal direction at 120° C. can be controlled byadjusting the temperature of cooling drum for cooling and solidifyingthe molten material to prepare an unstretched sheet, the conditions forthe longitudinal stretching (stretching temperature, stretching ratio,relaxation of the film after longitudinal stretching, etc.), thecrystallinity of the polypropylene (depending on meso pentad fraction(mmmm), isotactic index (II), etc.), the amount of the additive forproviding plasticity during stretching, and the like. The optimumlongitudinal-stretching conditions and raw materials should be selectedas needed, as long as the advantages are not impaired. More preferably,the heat shrinkage in the longitudinal direction at 120° C. is 4% orless.

In the biaxially stretched polypropylene film of the fifth embodiment,the sum of the heat shrinkage in the longitudinal direction (S(MD)) andthe heat shrinkage in the transverse direction at 120° C. is preferably8% or less. When the sum of the heat shrinkage in the longitudinal andtransverse directions exceeds 8%, an extensive degree of shrinkingoccurs when the film is heated during processes such as printing,laminating, coating, metallizing, and the like, resulting in processfailures such as defects in the film, pitch displacement, and the like.The index (II) of the fifth embodiment corresponds to this. The sum ofthe heat shrinkages in the longitudinal and transverse directions can becontrolled by adjusting the amount of the additive for providingplasticity during stretching and the like. The optimum film-formingconditions and raw materials should be selected as needed, as long asthe advantages are not impaired. More preferably, the sum of the heatshrinkage in the longitudinal (S(MD)) and the heat shrinkage in thetransverse directions at 120° C. is 6% or less.

The biaxially stretched polypropylene film preferably has a Young'smodulus in the longitudinal direction (Y(MD)) at 25° C. and a heatshrinkage in the longitudinal direction (S(MD)) at 120° C. that satisfythe formula below:Y(MD)≧S(MD)−1.The biaxially stretched polypropylene film that satisfies theabove-described formula can exhibit high tension resistance and superiorhandling convenience during film converting. When the above-describedformula is not satisfied, the biaxially stretched polypropylene film mayexhibit poor tension resistance during film converting or may induceprocess failures due to film shrinkage. In order to satisfy theabove-described formula, adjustment of the following may be performed:the film-forming conditions, e.g., the temperature of cooling drum forcooling and solidifying the molten material to prepare an unstretchedsheet, the temperatures during longitudinal/transverse stretching,stretching ratio, relaxation of the film after longitudinal/transversestretching; the crystallinity of the polypropylene (depending on mesopentad fraction (mmmm), isotactic index (II), etc.); the amount of theadditive for providing plasticity during stretching; and the like. Theoptimum film-forming conditions and raw materials should be selected asneeded, as long as advantages are not impaired. More preferably, theformula below is satisfied:Y(MD)≧S(MD)−0.7.

The water vapor permeability of the biaxially stretched polypropylenefilm of the fifth embodiment is preferably 1.5 g/m²/d/0.1 mm or less.When the water vapor permeability exceeds 1.5 g/m²/d/0.1 mm, thebiaxially stretched polypropylene film may exhibit poor moisture-proofproperty when it is used as a packaging material that shields thecontents from the external air, for example. The water vaporpermeability can be controlled by adjusting the film-forming conditions,e.g., the temperature of cooling drum for cooling and solidifying themolten material to prepare an unstretched sheet, the temperatures duringlongitudinal/transverse stretching, stretching ratio; the crystallinityof the polypropylene (depending on meso pentad fraction (mmmm),isotactic index (II), etc.); the amount of the additive for providingplasticity during stretching; and the like. The optimum film-formingconditions and raw materials should be selected as needed, as long asthe advantages are not impaired. More preferably, the water vaporpermeability is 1.2 g/m²/d/0.1 mm or less.

Publicly known methods may be employed in making the biaxially stretchedpolypropylene film. For example, a polypropylene which comprises apolypropylene satisfying the formula below,log(MS)>−0.61 log(MFR)+0.82,or a polypropylene which consists of a polypropylene satisfying theformula below,log(MS)>−0.61 log(MFR)+0.52,or a polypropylene which comprises having a Trouton ratio of 30 or more,or a polypropylene which consists of a polypropylene having a Troutonratio of 16 or more is blended with at least one of petroleum resinssubstantially containing no polar-group and/or terpene resinssubstantially containing no polar-group, and the mixture is fed into anextruder. The mixture is melted, filtered, and extruded from a slit die.The extruded mixture is then wound around a cooling drum to be cooledand solidified into a sheet to make an unstretched film. The temperatureof the cooling drum is preferably 20 to 100° C. so that the film can beadequately crystallized. In this manner, a large number of longitudinalfibrils having a large length can be obtained after biaxially stretcing.

Next, the resulting unstretched film is biaxially stretched by apublicly known longitudinal-transverse sequential biaxial stretchingmethod. The important factor for making a biaxially stretchedpolypropylene film highly tensilized in the longitudinal direction isthe stretching ratio in the longitudinal direction. The reallongitudinal stretching ratio in a conventional longitudinal-transversesequential biaxial stretching method for manufacturing a polypropylenefilm is in the range of 4.5 to 5.5, and when a longitudinal stretchingratio exceeds 6, film-forming may become unstable, and the film maybreak during transverse stretching. On the contrary, the reallongitudinal stretching ratio is preferably 6 or more. When an reallongitudinal stretching ratio is less than 6, sufficient longitudinalfibrils cannot be obtained, the stiffness in the longitudinal directionof the film may be insufficient, and the firmness of the resulting filmmay be insufficient in manufacturing thinner film. The more preferablereal stretching ratio in the longitudinal direction is 7 or more, andthe most preferable real stretching ratio is 8 or more. It is sometimespreferable to perform the longitudinal stretching in two or more stepsfrom the point of view of tensilization in the longitudinal directionand introduction of the longitudinal fibrils. The longitudinalstretching temperature is an optimum temperature selected from the pointof view of stability in film-forming, tensilization in the longitudinaldirection, and introduction of the longitudinal fibrils. Thelongitudinal stretching temperature is preferably 120 to 150° C.Moreover, during the cooling process that follows longitudinalstretching, the film is preferably relaxed in the longitudinal directionto an extent that does not further induce thickness irregularity of thefilm from the point of view of dimensional stability in the longitudinaldirection.

The real stretching ratio in the transverse direction is preferably 10or less. When an real transverse stretching ratio exceeds 10, thestiffness of the resulting film in the longitudinal direction may below, the number of longitudinal fibrils may decrease, and thefilm-forming may become unstable. The transverse stretching temperatureis an optimum temperature selected from the point of view of stabilityin film-forming, thickness irregularities, tensilization in thelongitudinal direction, and introduction of the longitudinal fibrils.The transversal stretching temperature is preferably 150 to 180° C.

After stretching in the transverse direction, the film is heat-set at150 to 180° C. while relaxing the film in the transverse direction by 1%or more, cooled, and wound to obtain the biaxially stretchedpolypropylene film.

An example method for manufacturing a film for metallization using abiaxially stretched polypropylene film will now be described. However,this disclosure is not limited by the manufacturing method describedbelow.

For example, a polypropylene which comprises a polypropylene satisfyingthe formula below:log(MS)>−0.61 log(MFR)+0.82or a polypropylene which consists of a polypropylene satisfying theformula below:log(MS)>−0.61 log(MFR)+0.52or a polypropylene which comprises a polypropylene having a Troutonratio of 30 or more, or a polypropylene which consists of apolypropylene having a Trouton ratio of 16 or more is blended with atleast one of petroleum resins substantially containing no polar-groupand/or terpene resins substantially containing no polar-group. The mixedresin and/or the third layer resin is prepared. These resins are fedinto separate extruders, melted at 200 to 290° C., and are filtered. Theresins are put together inside a short pipe or a die, extruded from aslit die to form a laminate each layer of which has a target thickness,and wound around a cooling drum to be cooled and solidified into a sheetto obtain an unstretched laminate film. The temperature of the coolingdrum is preferably 20 to 90° C. so that the film can be adequatelycrystallized. In this manner, a large number of longitudinal fibrilshaving a large length can be obtained after biaxially stretcing.

The unstretched laminate film is heated to a temperature of 120 to 150°C. and stretched in the longitudinal direction to 6 times the initiallength or more. The film is then fed into a tenter-type drawing machineso as to stretch the film in the transverse direction to 10 times theinitial length or less at 150 to 180° C., relaxed by heating at 150 to180° C., and cooled. If necessary, a surface of the base layer on whicha metallization layer is to be deposited and/or the third layer surfaceopposite of the base layer is subjected to corona discharge treatment inair, nitrogen, or mixture gas of carbon dioxide and nitrogen. When aheat-seal layer is to be laminated as a third layer, corona dischargetreatment is preferably avoided to achieve high adhesive strength. Next,the film is wound to obtain a biaxially stretched polypropylene film formetallization.

To make a film having a superior gas barrier property, theabove-described unstretched laminate film is heated to a temperature of120 to 150° C., stretched in the longitudinal direction to 6 times theinitial length or more, and cooled. Subsequently, the above-describedcoating material is applied on the uniaxially stretched film base layer.The base layer surface may be subjected to corona discharge treatment,if necessary. The film is then fed into a tenter-type drawing machine,stretched at a temperature of 150 to 180° C. in the transverse directionto 10 times the initial length or less, relaxed by heating at 150 to180° C., and cooled. The resulting coating layer on the base layerand/or the third layer surface opposite of the base layer may besubjected to corona discharge treatment in air, nitrogen, or mixture gasof carbon dioxide and nitrogen if necessary. At this stage, when aheat-seal layer is to be laminated as a third layer, corona dischargetreatment is preferably avoided to achieve high adhesive strength. Next,the film is wound to obtain a biaxially stretched polypropylene film formetallization.

The biaxially stretched polypropylene film for metallization ispreferably aged at 40 to 60° C. to accelerate the reaction in thecoating layer. When the reaction in the coating layer is accelerated,the adhesive strength of the coating layer to the base layer and to themetallization layer can be increased, and gas barrier property of thefilm can be improved. Aging is preferably performed for 12 hours ormore, and more preferably 24 hours or more to improve the chemicalresistance.

Next, the metallization is performed by vacuum metallization of metal. Ametal from evaporation source is deposited on the coating layer, whichcoats the surface of the biaxially stretched polypropylene film, to forma metallization layer.

Examples of the evaporation source include those of a resistance-heatingboat type, a radiation- or radiofrequency-heating crucible type, and anelectron beam heating type. The evaporation source is not restricted.

The metal used in the metallization is preferably a metal such as Al,Zn, Mg, Sn, Si, or the like. Alternatively, Ti, In, Cr, Ni, Cu, Pb, Fe,or the like may be used. These metal preferably has a purity of 99% ormore, and more preferably 99.5% or more and is preferably processed intograins, rods, tablets, wires, and crucibles.

Among the metals for metallization, an aluminum metallization layer ispreferably formed on at least one side of the film from the point ofview of durability of the metallization layer, production efficiency,and cost. Other metal components such as nickel, copper, gold, silver,chromium, zinc, and the like may be metallized sequentially orsimultaneously with aluminum.

The metallization layer preferably has a thickness of 10 nm or more, andmore preferably 20 nm or more to achieve high gas barrier property. Theupper limit of the thickness of the metallization layer is notrestricted; however, the thickness is preferably less than 50 nm fromthe point of view of economical and production efficiencies.

The gloss of the metallization layer is preferably 600% or more, andmore preferably 700% or more.

Alternatively, a metallization layer composed of metal oxide may beformed so that the film may be used as a transparent gas-barrier filmfor packaging having a superior gas barrier property. The metal oxidemetallization layer is preferably a layer of a metal oxide such asincompletely oxidized aluminum, or incompletely oxidized silicon.Incompletely oxidized aluminum is particularly preferable from the pointof view of durability of the metallization layer, production efficiency,and cost. Metallization can be performed by publicly known methods. Forexample, in depositing the metallization layer composed of incompletelyoxidized aluminum, the film is allowed to run in a high-vacuum devicehaving a degree of vacuum of 10⁻⁴ Torr or less, aluminum metal isheated, melted, and evaporated, and a small amount of oxygen gas issupplied at the site of evaporation so that the aluminum can becoherently deposited on the film surface to form a metallization layerwhile being oxidized. The thickness of the metal oxide metallizationlayer is preferably in the range of 10 to 50 nm, and more preferably 10to 30 nm. The oxidation of the metal oxide metallization layer composedof incompletely oxidized metal proceeds after metallization and changesthe light transmittance of the metal oxide metallization film. The lighttransmittance is preferably in the range of 70 to 90%. A lighttransmittance of less than 70% is not preferred since the content cannotbe seen through the package when the film is made into a packaging bag.A light transmittance exceeding 90% is not preferred because the gasbarrier property tends to be poor when the film is made into a packagingbag.

The adhesive strength between the metallization layer and the coatinglayer of the metallized biaxially stretched polypropylene film andbetween the metal oxide metallization layer and the coating layer of themetallized biaxially stretched polypropylene film is preferably 0.6 N/cmor more, and more preferably 0.8 N/cm or more. When the adhesivestrength is less than the above-described range, the metallization layermay be picked off when the metallized film is being wound into a rolland when the metallized film is being wound off for converting,resulting in degradation of the gas barrier property.

The gas barrier properties of the films prepared by depositing ametallization layer of a metal and an oxide metal on the biaxiallystretched polypropylene films are preferably as follows. The water vaporpermeability is preferably 4 g/m²/d or less, and more preferably 1g/m²/d or less, and the oxygen permeability is preferably 200ml/m²/d/MPa or less, and more preferably 100 ml/m²/d/MPa for use in foodpackaging bags.

The biaxially stretched polypropylene films of the first, second, third,fourth, and fifth embodiments have an increased stiffness in thelongitudinal direction compared with conventional biaxially stretchedpolypropylene films without degrading important properties such asdimensional stability and moisture-proof property. As a result, thefilms exhibit superior handling convenience and excellent tensionresistance against converting tension applied during film convertingsuch as printing, laminating, coating, metallizing, and bag-making.Moreover, the troubles such as cracks and print pitch displacement dueto the quality of base films can be avoided. Furthermore, the stiffnessin the longitudinal direction and the tension resistance are higher thanthose of the conventional polypropylenes having the same thickness;hence, the converting property can be maintained with a thicknesssmaller than that of conventional biaxially stretched polypropylenefilms. Accordingly, the biaxially stretched polypropylene films aresuitable for packaging and industrial use.

(Methods for Determined Characteristic Values)

The technical terms and the measurement methods employed in the presentinvention will now be described.

(1) Melt Strength (MS)

The melt strength MS was measured according to Japanese IndustrialStandards (JIS) K7210. A polypropylene was heated to 230° C. in amelt-tension tester available from Toyo Seiki Kogyo Co., Ltd., and themolten polypropylene was extruded at an extrusion speed of 15 mm/min tomake a strand. The tension of the strand at a take-over rate of 6.5m/min was measured, and this tension was defined as the melt strength(MS).

(2) Melt Flow Rate (MFR)

The melt flow rate was measured according to the polypropylene testingmethod of JIS K6758 at 230° C. and 2.16 kgf.

(3) Trouton Ratio

The Trouton ratio was measured by a converging flow method according toa theory by Cogswell [Polymer Engineering Science, 12, 64 (1972)] underthe following conditions:

Apparatus: twin-capillary rheometer RH-2200 (available from Rosand Inc.)

Temperature: 230° C.

Capillary size: Die/1.0 mm diam × 16 mm Orifice/1.0 mm diam × 0.25 mmShear rate: approximately 10 s⁻¹ to approximately 1800 s⁻¹ Extensionalstrain rate: approximately 2 s⁻¹ to approximately 180 s⁻¹

Each sample was fed into the apparatus and maintained at 230° C. for 3minutes. The sample was fed again and maintained for 3 minutes.Subsequently, the measurements were taken.

According to Cogswell's theory, the pressure drop of the converging flow(ΔP_(ent)) at the entrance of the capillary can be expressed in terms ofextensional viscosity and shear viscosity as the expression below:

${\Delta\; P_{ent}} = {\frac{4\sqrt{2}}{3\left( {n + 1} \right)}{\gamma_{a}\left( {\eta_{s}\eta_{E}} \right)}^{1/2}}$wherein η_(E): extensional viscosity, η_(s): shear viscosity, γ_(a):shear rate, and n is a flow index in the power law (σ_(s)=kγhd a^(n),σ_(s): shear stress)

With the twin-capillary rheometer, two capillaries of different lengthscan be simultaneously used so that the shear viscosity and ΔP_(ent) at aparticular shear rate can be simultaneously measured. The extensionalviscosity η_(E) can then be calculated from the equation below:

$\eta_{E} = {\frac{9\left( {n + 1} \right)^{2}}{32\;\eta_{s}}\left\lbrack \frac{\Delta\; P_{ent}}{\gamma_{a}} \right\rbrack}^{2}$$ɛ = \frac{4\;\eta_{s}\gamma_{a}^{2}}{3\left( {n + 1} \right)\Delta\; P_{ent}}$wherein ε: extensional stress. The obtained extensionalviscosity/extensional strain rate curve and shear viscosity/shear ratecurve were respectively approximated as exponential functions. Using theexponential functions, η_(E(60)) and η_(s(60)) at a strain rate of 60S⁻¹ were calculated. Based on these, the Trouton ratio at a strain rateof 60 s⁻¹ (the ratio of η_(E) to η_(s) at the same strain rate) wascalculated:Trouton ratio=η_(E(60))/η_(s(60))(4) Meso Pentad Fraction (mmmm)

A polypropylene was dissolved in o-dichlorobenzene-D6, and ¹³C-NMR wasmeasured at a resonance frequency of 67.93 MHz using JNM-GX270 apparatusavailable from JEOL Ltd. The assignment of the obtained spectrum and thecalculation of the meso pentad fraction were performed based on themethod by T. Hayashi et. al (Polymer, 29, 138-143 (1988)), in which, fora methyl-group-derived spectrum, each peaks were respectively assignedwith an mmmm peak of 21.855 ppm, the peak area was calculated, and theratio of the peak area to the total peak area of themethyl-group-derived peaks were calculated in terms of percentage. Thedetailed measurement conditions were as follows:

Measurement density: 15 to 20 wt. % Measurement solvent:o-dichlorobenzene (90 wt. %)/benzene-D6 (10 wt. %) Measurementtemperature: 120 to 130° C. Resonance frequency: 67.93 MHz Pulse width:10 microseconds (45° pulse) Pulse repeating time: 7.091 seconds Datapoints: 32K Number of accumulation: 8168 Measurement mode: Noisedecoupling(5) Young's Modulus, F2 Value, and F5 Value

The Young's modulus, F2 value, and F5 value at 25° C. were measured at65% RH using a film strength and elongation tester (AMF/RTA-100)available from Orientech Co., Ltd. A sample 15 cm in a measuringdirection and 1 cm in a direction perpendicular to the measuringdirection was prepared by cutting and was elongated at an originallength of 50 mm and a stretching rate of 300 mm/min. The Young's moduluswas measured according to JIS-Z1702. The F2 value and the F5 value were,respectively the stress applied on the sample at an elongation of 2% andat an elongation of 5%. When the measurement involves a hightemperature, such as 80° C., a hot/cold thermostat available from GondotScience, Ltd., under the same conditions described above.

(6) Observation of the Fibril Structure

A sample was placed in such a manner that the longitudinal direction ofthe sample matches with the vertical direction of an image, and was thenobserved with an atomic force microscope (AFM) under the conditiondescribed below. During observation, conditions such as gain andamplitude, etc. were suitably adjusted so that the image was notblurred. When blurring of the image was not corrected by adjusting theconditions, a cantilever was replaced. The sample was observed fivetimes each time at a different position for a field view of 1 μm (or 5μm, or 10 μm) square. A sample was evaluated as “A” when longitudinalfibrils having a width of 40 nm or more and extending across two sidesparallel to the transverse direction of the images were found in all ofthe five 10-μm square images. A sample was evaluated as “B” when suchlongitudinal fibrils were found in all of the five 5-μm square images,and a sample was evaluated as “C” when such longitudinal fibrils werefound in all of the five 1-μm images. A sample was evaluated as “NONE”when no longitudinal fibrils having a width of 40 nm or more wereobserved. The number and the width of the longitudinal fibrils of thesample were calculated and averaged from the number and the width of thelongitudinal fibrils having a width of 40 nm or more in each images.Note that it is preferable to observe both surfaces of the film;however, it is sufficient to observe only one surface of the film.

Apparatus: NanoScope III AFM (manufactured by Digital Instruments, Co.)Cantilever: Single crystal of silicon Scan mode: Tapping mode Scanrange: 1 μm × 1 μm, 5 μm × 5 μm, 10 μm × 10 μm Scan rate: 0.3 Hz(7) Isotactic Index (II)

A polypropylene was extracted with 60° C. or lower n-heptane for 2 hoursso as to remove the additives in the polypropylene, and was subsequentlyvacuum-dried at 130° C. for 2 hours. A sample of weight W (mg) was takentherefrom, and extracted with boiled n-heptane in a Soxhlet extractorfor 12 hours. The sample was then taken out, sufficiently washed withacetone, and vacuum-dried at 130° C. for 6 hours. The sample was thencooled to normal temperature, and the weight W′ (mg) was measured. Theisotactic index was then determined with the following equation:II=(W′/W)×100 (%)(8) Intrinsic Viscosity ([η])

A polypropylene was dissolved in tetralin at 135° C., and the intrinsicviscosity was measured with an Ostwald viscometer manufactured by MitsuiToatsu Chemicals, Inc.

(9) Glass Transition Temperature (Tg)

Into a thermal analysis apparatus RDC 220 available from SeikoInstruments, Inc., 5 mg of a sample enclosed in an aluminum pan was fed,and the temperature was increased at a rate of 20° C./min. Using theinternal program of a thermal analysis system SSC5200 available fromSeiko Instruments, Inc., the starting point of glass transition wasdetermined from the resulting thermal curve and this temperature wasdefined as the glass transition temperature (Tg).

(10) Bromine Number

The bromine number was measured according to JIS K2543-1979. The numberof grams of bromine added to the unsaturated components in a 100-g ofsample oil was defined as the bromine number.

(11) Heat Shrinkage

The measurement was performed in the longitudinal direction and in thetransverse direction. A film sample having a length of 260 mm and awidth of 10 mm was prepared, and a mark was placed at a positioncorresponding to a length of 200 mm, i.e., the original length L₀. Thesample was heated at 120° C. for 15 minutes in a heat flow convectionoven while being applied with a load of 3 g at the lower end of thesample. The sample was then discharged into room temperature, and themarked length (L₁) of the sample was measured. The heat shrinkage wascalculated by the equation below. This process was performed for eachdirection (longitudinal direction and transverse direction), and the sumof the heat shrinkages in the longitudinal direction and the transversedirection was calculated.Heat shrinkage (%)=100×(L ₀ −L ₁)/L ₀(12) Centerline Average Roughness (Ra)

The centerline average roughness (Ra) was measured according to JISB0601 using stylus-type roughness meter. A high-accuracy thin-filmstep-difference measuring instrument (type:ET-30HK), manufactured byKosaka Laboratory Ltd., was used. The conical stylus had a radius of 0.5μm, the load was 16 mg, and the cut-off was 0.08 mm.

The portion of the roughness curve corresponding to the measurementlength L was cut off in the center line direction, and the centerlineaverage roughness (Ra) in terms of μm was calculated by the equationbelow, wherein the centerline of the portion cut off is the X axis, thelongitudinal direction of the portion cut off is the Y axis, and theroughness curve is represented by y=f(x):

${R\; a} = {\frac{1}{L}{\int{{{f(x)}}{\mathbb{d}x}}}}$(13) Thickness of the Coating Layer, Metallization Layer, and MetalOxide Metallization Layer

Using a transmission electron microscope (TEM), the structure of a filmcross-section was observed, and the thickness of the deposited layer andthe thickness constructions were measured.

(14) Surface Gloss of the Film

The surface gloss of the film as a 60° specular gloss was measured witha digital variable angle gloss meter UGV-5D manufactured by Suga TestInstruments Co., Ltd. according to JIS Z8741 method.

(15) Surface Gloss of the Metallized Film

A metallized biaxially stretched polypropylene film was installed in acontinuous vacuum metallizing apparatus. While allowing aluminum toevaporate from an electron-beam heating type evaporation source andallowing the film to run continuously, aluminum was deposited so thatthe optical density (−log(optical transmittance)) measured using a anoptical densitometer (TR927) manufactured by Macbeth was in the range of1.9 to 2.1. The surface gloss of the metallized film was measuredaccording to JIS Z8741.

(16) Adhesive Strength

The adhesive strength between the surface layer of the biaxiallystretched polypropylene film and the coating layer after metallizationwas measured as below. A biaxially oriented polypropylene film having athickness of 20 μm (S645, manufactured by Toray Industries, Inc.) waslaminated on the side of the coating layer using a polyurethane-basedadhesive, and was left to stand at 40° C. for 48 hours. A 90° peel at apeeling rate of 10 cm/min was performed at a width of 15 mm usingTensilon manufactured by Toyo Baldwin Co. Ltd. The adhesive strengthsbetween the polypropylene film for metallization and the metallizationlayer and that between the polypropylene film for metallization and themetal oxide metallization layer are measured by the same methoddescribed above in which a biaxially oriented polypropylene film havinga thickness of 20 μm (S645, manufactured by Toray Industries, Inc.) waslaminated on the side of the metallization layer and on the side of themetal oxide metallization layer using a polyurethane-based adhesive.

(17) Oxygen Permeability

A polypropylene adhesive film (Scotchmark, manufactured by 3M Company,40 μm in thickness) was attached on the metallized side of a biaxiallystretched polypropylene film, and the oxygen permeability was measuredat 23° C. and a relative humidity of 0% using an oxygen permeabilitymeasuring instrument Oxtran 2/20 manufactured by MOCON/Modern ControlsInc.

(18) Water Vapor Permeability

The water vapor permeability of a biaxially stretched polypropylene filmwas measured at 40° C. and a relative humidity of 90% using a watervapor permeability measuring instrument PERMATRAN-W3/30 manufactured byMOCON/Modern Controls Inc. The water vapor permeability of a metallizedbiaxially stretched polypropylene film was measured as described abovebut with a polypropylene adhesive film (Scotchmark, manufactured by 3MCompany, 40 μm in thickness) attached on the metallized side.

(19) Real Stretching Ratio

An unstretched film was prepared by extruding a material from a slit dieand winding the extruded material on a metal drum so as to be cooled andsolidified into a sheet. A 1-cm square mark the sides of which extend inthe longitudinal and transverse direction of the film was inscribed onthe unstretched film, and the unstretched film was stretched and wound.Subsequently, the length (cm) of the inscribed square mark on the filmwas measured, and the real stretching ratios in the longitudinaldirection and the transverse direction were determined.

(20) Converting Ability

An unstretched polypropylene film having a thickness of 20 μm waslaminated on a biaxially stretched polypropylene film or a metallizedbiaxially stretched polypropylene film (on the opposite side of themetallization layer) of the present invention having a length of 1,000 mand a thickness of 15 μm so as to prepare a food-packaging film. Withthe unstretched polypropylene film facing inward, the film was installedin a cylindrical manner using a vertical-type pillow-packaging machine(Fuji FW-77) manufactured by Fuji Machinery Co., Ltd., and was formedinto bags.

In bag-making, a film that did not have wrinkles or elongated portionsand that was processed into bags with good appearance was evaluated as“good”. A film that was processed into bags with poor appearance sincethe bag had elongated portions due to a low Young's modulus of the filmin the longitudinal direction and low firmness, or since the bag hadwrinkles due to a poor slipperiness and a large heat shrinkage, wasevaluated as “poor”.

EXAMPLES

The films will now be described based on Examples. Unless otherwisenoted, the screw speed of the extruder and the rotating speed of thecooling drum were adjusted to predetermined values to obtain a filmhaving a desired thickness.

Example 1

To 90 percent by weight of a polypropylene prepared by blending apublicly known polypropylene having a melt strength (MS) of 1.5 cN, amelt flow rate (MFR) of 2.3 g/10 min, a meso pentad fraction (mmmm) of92%, and an isotactic index (II) of 96% with 10 percent by weight of ahigh-melt-strength polypropylene (HMS-PP) having a melt strength of 20cN, a melt flow rate (MFR) of 3 g/10 min, a meso pentad fraction (mmmm)of 97%, and an isotactic index (II) of 96.5%, containing long-chainbranches, and satisfying the above-described formula (1) between themelt strength (MS) and the melt flow rate (MFR), 10 percent by weight ofpolydicyclopentadiene having Tg of 80° C., a bromine number of 3 cg/g,and a hydrogenation rate of 99%, which is a petroleum resinsubstantially containing no polar-group, was added as an additive thathas compatibility with the polypropylene and can provide plasticityduring stretching to prepare a resin. To 100 parts by weight of thisresin, 0.15 parts by weight of crosslinked particles of apolymethacrylicacid-based polymer (crosslinked PMMA) having an averageparticle size of 2 μm was added as crosslinked organic particles, and0.8 parts by weight of a 1:1 mixture of glycerin fatty acid ester andalkyldiethanolamine fatty acid ester was added as an antistatic agent.The resulting mixture was fed into a twin-screw extruder, was extrudedat 240° C. into a gut-shape, cooled in a 20° C. water bath, and cut intoa 3-mm length by a chip cutter. The resulting chips were dried for 2hours at 100° C., fed into a single-screw extruder, melted at 260° C.,and filtered. The resulting filtered material was extruded from a slitdie and formed into a sheet by winding on a metal drum having atemperature of 25° C.

This sheet was passed between rolls maintained at 135° C., andpre-heated, and passed between rolls, which had different rotating speedand were maintained at 140° C., so that the sheet is stretched to 8times the initial length in the longitudinal direction. The stretchedsheet was then immediately cooled to room temperature. The stretchedfilm was next fed into a tenter to be pre-heated at 165° C., stretchedin the transverse direction to 7 times the initial length at 160° C.,and heat-set at 160° C. while being relaxed in the transverse directionby 6%. The film was then cooled and wound so as to obtain a biaxiallystretched polypropylene film having a thickness of 15 μm.

The composition of the raw material and the results of the evaluation ofthe film characteristics are shown in Tables 1 and 2. The resulting filmhad a high Young's modulus in the longitudinal direction and superiortension resistance, dimensional stability, moisture-proof property, andconverting ability.

Example 2

A biaxially stretched polypropylene film of EXAMPLE 2 having a thicknessof 15 μm was prepared as in EXAMPLE 1 except that a stretching ratio inthe longitudinal direction was increased to 10.

The results are shown in Tables 1 and 2. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 3

A biaxially stretched polypropylene film of EXAMPLE 3 having a thicknessof 15 μm was prepared as in EXAMPLE 1 except that 5 percent by weight ofthe HMS-PP having long-chain branches was blended and 3 percent byweight of polydicyclopentadiene was added. Moreover, the film wasstretched to 8 times the initial length in the longitudinal directionand to 8 times the initial length in the transverse direction.

The results are shown in Tables 1 and 2. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 4

A biaxially stretched polypropylene film of EXAMPLE 4 having a thicknessof 15 μm was prepared as in EXAMPLE 3 except that 3 percent by weight ofthe HMS-PP having long-chain branches was blended.

The results are shown in Tables 1 and 2. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 5

A biaxially stretched polypropylene film of EXAMPLE 5 having a thicknessof 15 μm was prepared as in EXAMPLE 1 except that 5 percent by weight ofβ-pinene having a Tg of 75° C., a bromine number of 4 cg/g, and ahydrogenation rate of 99%, which is a terpene resin substantiallycontaining no polar-group, was added as an additive that has acompatibility with the polypropylene and can provide plasticity duringstretching, and that the film is stretched to 9 times the initial lengthin the longitudinal direction and to 7 times the initial length in thetransverse direction.

The results are shown in Tables 1 and 2. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 6

To 100 parts by weight of a resin composition containing 85 percent byweight of a HMS-PP containing long-chain branches and having a meltstrength (MS) of 20 cN, a melt flow rate (MFR) of 3 g/10 min, a mesopentad fraction (mmmm) of 97%, and an isotactic index (II) of 96.5%, andsatisfying the formula below between the melt strength (MS) and the meltflow rate (MFR)log(MS)>−0.61 log(MFR)+0.82and 15 percent by weight of hydrogenated β-dipentene having a Tg of 75°C., a bromine number of 3 cg/g, and a hydrogenation rate of 99%, whichwas a terpene resin substantially containing no polar-group, as anadditive that has a compatibility with the polypropylene and can provideplasticity during stretching, 0.15 parts by weight of crosslinkedparticles of polystyrene-based polymer (crosslinked PS) having anaverage particle size of 1 μm was added as crosslinked organicparticles. Furthermore, 0.8 parts by weight of a 1:1 mixture of glycerinfatty acid ester and alkyldiethanolamine fatty acid ester was added asan antistatic agent. The resulting mixture was fed into a twin-screwextruder, was extruded at 240° C. into a gut-shape, cooled in a 20° C.water bath, and cut into a 3-mm length by a chip cutter. The resultingchips were dried for 2 hours at 100° C., fed into a single-screwextruder, melted at 260° C., and filtered. The resulting filteredmaterial was extruded from a slit die and formed into a sheet by windingon a metal drum having a temperature of 30° C.

This sheet was passed between rolls maintained at 133° C., andpre-heated, and passed between rolls, which had different rotating speedand were maintained at 138° C., so that the sheet is stretched to 8times the initial length in the longitudinal direction. The stretchedsheet was then immediately cooled to room temperature. The stretchedfilm was next fed into a tenter to be pre-heated at 163° C., stretchedin the transverse direction to 8 times the initial length at 160° C.,and heat-set at 160° C. while being relaxed in the transverse directionby 8%. The film was then cooled and wound so as to obtain a biaxiallystretched polypropylene film having a thickness of 15 μm.

The results are shown in Tables 1 and 2. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 7

A biaxially stretched polypropylene film having a thickness of 15 μm wasprepared as in EXAMPLE 6 except that to 80 percent by weight of apolypropylene prepared by blending a publicly known polypropylene havinga melt strength (MS) of 1.5 cN, a melt flow rate (MFR) of 2.3 g/10 min,a meso pentad fraction (mmmm) of 92%, and an isotactic index (II) of 96%with 5 percent by weight of a HMS-PP having a melt strength (MS) of 20cN, a melt flow rate (MFR) of 3 g/10 min, a meso pentad fraction (mmmm)of 97%, and an isotactic index (II) of 96.5%, containing long-chainbranches, and satisfying the above-described formula (1) between themelt strength (MS) and the melt flow rate (MFR), 20 percent by weight ofa mixture containing β-pinene having a Tg of 75° C., a bromine number of4 cg/g, and a hydrogenation rate of 99% and hydrogenated β-dipenteneresin having a Tg of 75° C., a bromine number of 3 cg/g, and ahydrogenation rate of 99%, which are terpene resins substantiallycontaining no polar-group, as additives that has a compatibility withthe polypropylene and can provide plasticity during stretching.Moreover, the film was stretched to 11 times the initial length in thelongitudinal direction, and to 6 times the initial length in thetransverse direction.

The results are shown in Tables 1 and 2. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 8

A biaxially stretched polypropylene film of EXAMPLE 8 having a thicknessof 15 μm was prepared as in EXAMPLE 3, except that a HMS-PP thatcontains long-chain branches and has a melt strength (MS) of 15 cN, amelt flow rate (MFR) of 2.0 g/10 min, a meso pentad fraction (mmmm) of96.5%, and an isotactic index (II) of 97%, satisfies the above-describedformula (1) between the melt strength (MS) and the melt flow rate (MFR),was used as the HMS-PP.

The results are shown in Tables 1 and 2. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 9

A biaxially stretched polypropylene film of EXAMPLE 9 having a thicknessof 15 μm was prepared as in EXAMPLE 3, except that a HMS-PP containinglong-chain branches, and having a melt strength (MS) of 30 cN, a meltflow rate (MFR) of 2.1 g/10 min, a meso pentad fraction (mmmm) of 97%,and an isotactic index (II) of 97%, and satisfying the formula belowbetween the melt strength (MS) and the melt flow rate (MFR) was used asthe HMS-PP:log(MS)>−0.61 log(MFR)+0.82

The results are shown in Tables 1 and 2. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 10

A biaxially stretched polypropylene film of EXAMPLE 10 having athickness of 15 μm was prepared as in EXAMPLE 5, except that 20 percentby weight of HMS-PP containing long-chain branches was blended, and thatpolydicyclopentadiene having Tg of 80° C., a bromine number of 3 cg/g,and a hydrogenation rate of 99%, which is a petroleum resinsubstantially containing no polar-group, as an additive that hascompatibility with the polypropylene and can provide plasticity duringstretching, was added.

The results are shown in Tables 1 and 2. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 11

A biaxially stretched polypropylene film of EXAMPLE 11 having athickness of 15 μm was prepared as in EXAMPLE 10 except that 30 percentby weight of HMS-PP was blended.

The results are shown in Tables 1 and 2. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 12

A biaxially stretched polypropylene film of EXAMPLE 12 having athickness of 15 μm was prepared as in EXAMPLE 10 except that 50 percentby weight of HMS-PP was added.

The results are shown in Tables 1 and 2. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 13

A biaxially stretched polypropylene film of EXAMPLE 13 having athickness of 15 μm was prepared as in EXAMPLE 1 except that an HMS-PPcontaining long-chain branches and having a melt strength (MS) of 1 cN,a melt flow rate (MFR) of 10 g/10 min, a meso pentad fraction (mmmm) of98%, and an isotactic index (II) of 98.5%, was blended.

The results are shown in Tables 1 and 2. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 14

A biaxially stretched polypropylene film of EXAMPLE 14 having athickness of 15 μm was prepared as in EXAMPLE 1 except that apolypropylene prepared by blending a publicly known polypropylene havinga melt strength (MS) of 1.1 cN, a melt flow rate (MFR) of 3 g/10 min, ameso pentad fraction (mmmm) of 97.5%, and an isotactic index (II) of 99%with 10 percent by weight of the HMS-PP was used. Moreover, the film wasstretched to 9 times the initial length in the longitudinal directionand 9 times the initial length in the transverse direction.

The results are shown in Tables 1 and 2. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 15

A biaxially stretched polypropylene film of EXAMPLE 15 having athickness of 15 μm was prepared as in EXAMPLE 3 except that apolypropylene prepared by blending a publicly known polypropylene havinga melt strength (MS) of 1.2 cN, a melt flow rate (MFR) of 2.7 g/10 min,a meso pentad fraction (mmmm) of 96%, and an isotactic index (II) of 98%with 5 percent by weight of the HMS-PP was used.

The results are shown in Tables 1 and 2. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

TABLE 1 Characteristics of polypropylene resin Characteristics of HMS-PPresin MS MFR −0.61log(MFR) formula (1) Content (cN) (g/10 min) log(MS)+0.82 satisfied? (wt. %) EXAMPLE 1 20.0 3.0 1.30 0.53 Yes 10 EXAMPLE 220.0 3.0 1.30 0.53 Yes 10 EXAMPLE 3 20.0 3.0 1.30 0.53 Yes 5 EXAMPLE 420.0 3.0 1.30 0.53 Yes 3 EXAMPLE 5 20.0 3.0 1.30 0.53 Yes 10 EXAMPLE 620.0 3.0 1.30 0.53 Yes 100 EXAMPLE 7 20.0 3.0 1.30 0.53 Yes 5 EXAMPLE 815.0 2.0 1.18 0.64 Yes 5 EXAMPLE 9 30.0 2.1 1.48 0.62 Yes 5 EXAMPLE 1020.0 3.0 1.30 0.53 Yes 20 EXAMPLE 11 20.0 3.0 1.30 0.53 Yes 30 EXAMPLE12 20.0 3.0 1.30 0.53 Yes 50 EXAMPLE 13 1.0 10.0 0.00 0.21 No 10 EXAMPLE14 20.0 3.0 1.30 0.53 Yes 10 EXAMPLE 15 20.0 3.0 1.30 0.53 Yes 5Characteristics of polypropylene resin Meso Pentad MS MFR −0.61log(MFR)formula (2) Fraction (cN) (g/10 min) log(MS) +0.52 satisfied? (%)EXAMPLE 1 3.0 2.3 0.48 0.30 Yes 92.5 EXAMPLE 2 3.0 2.3 0.48 0.30 Yes92.5 EXAMPLE 3 2.7 2.2 0.43 0.31 Yes 92.3 EXAMPLE 4 2.4 2.3 0.38 0.30Yes 92.2 EXAMPLE 5 3.0 2.3 0.48 0.30 Yes 92.5 EXAMPLE 6 20.0 3.0 1.300.23 Yes 97.0 EXAMPLE 7 2.7 2.2 0.43 0.31 Yes 92.5 EXAMPLE 8 2.6 2.20.41 0.31 Yes 92.2 EXAMPLE 9 3.4 2.2 0.53 0.31 Yes 92.3 EXAMPLE 10 3.32.4 0.52 0.29 Yes 93.0 EXAMPLE 11 3.6 2.4 0.56 0.29 Yes 93.5 EXAMPLE 123.5 2.5 0.54 0.28 Yes 94.5 EXAMPLE 13 2.0 3.0 0.30 0.23 Yes 92.6 EXAMPLE14 2.7 3.0 0.43 0.23 Yes 97.5 EXAMPLE 15 2.8 2.7 0.45 0.26 Yes 96.1Content Petroleum resin and Content Stretching ratio (wt. %) terpeneresin (wt. %) (longitudinal × transverse) EXAMPLE 1 90 hydrogenated 10 8× 7 dicyclopentadiene EXAMPLE 2 90 hydrogenated 10 10 × 6 dicyclopentadiene EXAMPLE 3 97 hydrogenated 3 8 × 8 dicyclopentadieneEXAMPLE 4 97 hydrogenated 3 8 × 8 dicyclopentadiene EXAMPLE 5 95hydrogenated β- 5 9 × 7 pinene EXAMPLE 6 85 hydrogenated β- 15 8 × 8dipentene EXAMPLE 7 80 hydrogenated β- 20 11 × 6  pinene andhydrogenated β- dipentene EXAMPLE 8 97 hydrogenated 3 8 × 8dicyclopentadiene EXAMPLE 9 97 hydrogenated 3 8 × 8 dicyclopentadieneEXAMPLE 10 95 hydrogenated 5 9 × 7 dicyclopentadiene EXAMPLE 11 95hydrogenated 5 9 × 7 dicyclopentadiene EXAMPLE 12 95 hydrogenated 5 9 ×7 dicyclopentadiene EXAMPLE 13 90 hydrogenated 10 8 × 7dicyclopentadiene EXAMPLE 14 90 hydrogenated 10 9 × 9 dicyclopentadieneEXAMPLE 15 97 hydrogenated 3 8 × 8 dicyclopentadiene

TABLE 2 Young's Young's modulus modulus F2 value F5 value (longitudinal)(transverse) m value at (longitudinal) (longitudinal) at 25° C. at 25°C. 25° C. at 25° C. at 25° C. (GPa) (GPa) (−) (MPa) (Mpa) EXAMPLE 1 3.74.2 0.47 60 82 EXAMPLE 2 4.3 3.5 0.55 72 103 EXAMPLE 3 3.1 3.5 0.47 4864 EXAMPLE 4 2.7 3.8 0.42 43 55 EXAMPLE 5 3.6 3.7 0.49 58 87 EXAMPLE 64.0 3.7 0.52 61 92 EXAMPLE 7 5.2 4.7 0.53 80 115 EXAMPLE 8 2.9 3.8 0.4345 58 EXAMPLE 9 3.5 3.3 0.51 58 74 EXAMPLE 10 3.4 3.5 0.49 51 63 EXAMPLE11 3.3 3.6 0.48 50 63 EXAMPLE 12 3.1 3.1 0.50 47 60 EXAMPLE 13 2.6 3.70.41 41 53 EXAMPLE 14 3.6 4.2 0.46 63 79 EXAMPLE 15 3.3 4.0 0.45 53 65Young's modulus Young's modulus (longitudinal) (transverse) at at 80° C.(GPa) 80° C. (GPa) m value at 80° C. (−) EXAMPLE 1 0.59 0.65 0.48EXAMPLE 2 0.65 0.58 0.53 EXAMPLE 3 0.50 0.48 0.51 EXAMPLE 4 0.45 0.500.47 EXAMPLE 5 0.58 0.55 0.51 EXAMPLE 6 0.67 0.70 0.49 EXAMPLE 7 0.800.75 0.52 EXAMPLE 8 0.47 0.58 0.45 EXAMPLE 9 0.53 0.48 0.52 EXAMPLE 100.56 0.50 0.53 EXAMPLE 11 0.57 0.52 0.52 EXAMPLE 12 0.60 0.53 0.53EXAMPLE 13 0.42 0.48 0.47 EXAMPLE 14 0.78 0.65 0.55 EXAMPLE 15 0.69 0.680.50 Heat Heat shrinkage shrinkage Sum of heat Water vapor(longitudinal) (transverse) at shrinkage at permeability at 120° C. 120°C. 120° C. (g/m²/d/0.1 Converting (%) (%) (%) mm) ability EXAMPLE 1 3.30.6 3.9 0.8 Good EXAMPLE 2 4.0 1.0 5.0 0.7 Good EXAMPLE 3 3.0 0.5 3.51.2 Good EXAMPLE 4 3.1 0.6 3.7 1.3 Good EXAMPLE 5 3.0 0.7 3.7 1.0 GoodEXAMPLE 6 2.9 0.7 3.6 0.8 Good EXAMPLE 7 4.2 1.5 5.7 0.5 Good EXAMPLE 82.5 0.6 3.1 1.2 Good EXAMPLE 9 3.1 0.5 3.6 1.1 Good EXAMPLE 10 3.0 0.53.5 1.0 Good EXAMPLE 11 2.9 0.5 3.4 1.0 Good EXAMPLE 12 2.9 0.4 3.3 0.9Good EXAMPLE 13 3.0 1.0 4.0 0.8 Good EXAMPLE 14 1.6 0.3 1.9 0.5 GoodEXAMPLE 15 1.5 0.2 1.7 1.2 Good

Comparative Example 1

To 100 parts by weight of a publicly known polypropylene having a meltstrength (MS) of 1.5 cN, a melt flow rate (MFR) of 2.3 g/10 min, a mesopentad fraction (mmmm) of 92%, and an isotactic index (II) of 96%, notsatisfying the above-described formula (2) between the melt strength(MS) and the melt flow rate (MFR), 0.15 parts by weight of crosslinkedparticles of a polymethacrylicacid-based polymer (crosslinked PMMA)having an average particle size of 2 μm was added as crosslinked organicparticles, and 0.8 parts by weight of a 1:1 mixture of glycerin fattyacid ester and alkyldiethanolamine fatty acid ester was added as anantistatic agent. The mixture was fed into a singlescrew extruder,melted at 260° C., filtered, extruded from a slit die, and formed into asheet by winding around a 25° C. metal drum.

This sheet was passed between rolls maintained at 130° C., andpre-heated, and passed between rolls, which had different rotating speedand were maintained at 135° C., so that the sheet is stretched to 5times the initial length in the longitudinal direction. The stretchedsheet was then immediately cooled to room temperature. The stretchedfilm was next fed into a tenter to be pre-heated at 165° C., stretchedin the transverse direction to 10 times the initial length at 160° C.,and heat-set at 160° C. while being relaxed in the transverse directionby 7%. The film was then cooled and wound so as to obtain a biaxiallystretched polypropylene film having a thickness of 15 μm.

The results are shown in Tables 3 and 4. The resulting film had a lowYoung's modulus in the longitudinal direction, poor tension resistance,moisture-proof property, and converting ability.

Comparative Example 2

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 2 havinga thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 1 exceptthat the stretching ratio in the longitudinal direction was increased to7.

The results are shown in Tables 3 and 4. Because a significant degree offilm breakage occurred during transverse stretching, the sufficient filmcouldn't be obtained.

Comparative Example 3

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 3 havinga thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 1 exceptthat a publicly known polypropylene having a melt strength (MS) of 1.1cN, a melt flow rate (MFR) of 3 g/10 min, a meso pentad fraction (mmmm)of 97.5%, and an isotactic index (II) of 99% was used.

The results are shown in Tables 3 and 4. Because the edges of the filmrode up when the film in the molten state was wound on a cooling drum,the sheet frequently broke during longitudinal stretching. Moreover,film breakage occurred during transverse stretching, overall filmformability was poor, and the film was not suited for industrialproduction.

Comparative Example 4

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 4 havinga thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 1 exceptthat a publicly known polypropylene having a melt strength (MS) of 0.6cN, a melt flow rate (MFR) of 6 g/10 min, a meso pentad fraction (mmmm)of 99.8%, and an isotactic index (II) of 99.5% was used.

The results are shown in Tables 3 and 4. Because a significant degree offilm breakage occurred during transverse stretching, the sufficient filmcouldn't be obtained.

Comparative Example 5

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 5 havinga thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 1 exceptthat 3 percent by weight of polydicyclopentadiene having Tg of 80° C., abromine number of 3 cg/g, and a hydrogenation rate of 99%, which is apetroleum resin substantially containing no polar-group as an additivethat has compatibility with the polypropylene and can provide plasticityduring stretching. Moreover, the film was stretched to 5 times theinitial length in the longitudinal direction and 9 times the initiallength in the transverse direction.

The results are shown in Tables 3 and 4. The resulting film had a lowYoung's modulus in the longitudinal direction, poor tension resistanceand converting ability.

Comparative Example 6

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 6 havinga thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 5 exceptthat the film was stretched to 7 times the initial length in thelongitudinal direction and 8 times the initial length in the transversedirection.

The results are shown in Tables 3 and 4. Because film breakage occurredduring transversal stretching, a film having a sufficient length couldnot be obtained, and the film was not suited for industrial production.

Comparative Example 7

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 7 havinga thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 5 exceptthat the stretching ratio in the longitudinal direction was increased to8.

The results are shown in Tables 3 and 4. Because a significantly degreeof film breakage occurred during transverse stretching, the sufficientfilm could not be obtained.

Comparative Example 8

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 8 havinga thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 5 exceptthat 10 percent by weight of polydicyclopentadiene was added.

The results are shown in Tables 3 and 4. The resulting film had a lowYoung's modulus in the longitudinal direction at 80° C., poor tensionresistance, dimensional stability, and converting ability.

Comparative Example 9

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 9 havinga thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 8 exceptthat the film was stretched to 8 times the initial length in thelongitudinal direction and 7 times the initial length in the transversedirection.

The results are shown in Tables 3 and 4. Because film breakage occurredduring transverse stretching, a film having a sufficient length couldnot be obtained, and the film was not suited for industrial production.

Comparative Example 10

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 10having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 8except that the stretching ratio in the longitudinal direction wasincreased to 9.

The results are shown in Tables 3 and 4. Because a significant degree offilm breakage occurred during transverse stretching, sufficient filmcould not be obtained.

Comparative Example 11

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 11having a thickness of 15 μm was prepared as in EXAMPLE 6 except thatonly the HMS-PP containing long-chain branches, satisfying theabove-described formula (1) between the melt strength (MS) and the meltflow rate (MFR), was used. Moreover, the film was stretched to 5 timesthe initial length in the longitudinal direction and 11 times theinitial length in the transverse direction.

The results are shown in Tables 3 and 4. The resulting film had a lowYoung's modulus in the longitudinal direction, and poor tensionresistance and converting ability.

Comparative Example 12

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 12having a thickness of 15 μm was prepared as in EXAMPLE 5 except thatunhydrogenated gum rosin having Tg of 39° C. and a bromine number of 15cg/g and containing polar carboxyl groups that have poor compatibilitywith the polypropylene was used instead of the petroleum resinsubstantially containing no polar-group. Moreover, the film wasstretched to 5 times the initial length in the longitudinal directionand 11 times the initial length in the transverse direction.

The results are shown in Tables 3 and 4. The resulting film had a lowYoung's modulus in the longitudinal direction, and poor tensionresistance and converting ability.

Comparative Example 13

A uniaxially stretched polypropylene film of COMPARATIVE EXAMPLE 13having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 1except that the film was stretched to 8 times the initial length in thelongitudinal direction and was directly wounded right after cooling.

The results are shown in Tables 3 and 4. The film readily split alonglines parallel to the longitudinal direction, had poor handlingconvenience, and poor converting ability.

TABLE 3 Characteristics of polypropylene resin Characteristics of HMS-PPresin MS MFR −0.61log(MFR) formula (1) Content (cN) (g/10 min) log(MS)+0.82 satisfied? (wt. %) COMPARATIVE — — — — — — EXAMPLE 1 COMPARATIVE —— — — — — EXAMPLE 2 COMPARATIVE — — — — — — EXAMPLE 3 COMPARATIVE — — —— — — EXAMPLE 4 COMPARATIVE — — — — — — EXAMPLE 5 COMPARATIVE — — — — —— EXAMPLE 6 COMPARATIVE — — — — — — EXAMPLE 7 COMPARATIVE — — — — — —EXAMPLE 8 COMPARATIVE — — — — — — EXAMPLE 9 COMPARATIVE — — — — — —EXAMPLE 10 COMPARATIVE 20.0 3.0 1.30 0.53 Yes 100 EXAMPLE 11 COMPARATIVE20.0 3.0 1.30 0.53 Yes  10 EXAMPLE 12 COMPARATIVE — — — — — — EXAMPLE 13Characteristics of polypropylene resin Meso pentad MS MFR −0.61log(MFR)formula (2) fraction (cN) (g/10 min) log(MS) +0.52 satisfied? (%)COMPARATIVE 1.5 2.3 0.18 0.30 No 92.0 EXAMPLE 1 COMPARATIVE 1.5 2.3 0.180.30 No 92.0 EXAMPLE 2 COMPARATIVE 1.1 3.0 0.04 0.23 No 97.5 EXAMPLE 3COMPARATIVE 0.6 6.0 −0.22   0.05 No 99.8 EXAMPLE 4 COMPARATIVE 1.5 2.30.18 0.30 No 92.0 EXAMPLE 5 COMPARATIVE 1.5 2.3 0.18 0.30 No 92.0EXAMPLE 6 COMPARATIVE 1.5 2.3 0.18 0.30 No 92.0 EXAMPLE 7 COMPARATIVE1.5 2.3 0.18 0.30 No 92.0 EXAMPLE 8 COMPARATIVE 1.5 2.3 0.18 0.30 No92.0 EXAMPLE 9 COMPARATIVE 1.5 2.3 0.18 0.30 No 92.0 EXAMPLE 10COMPARATIVE 20.0  3.0 1.30 0.23 Yes 97.0 EXAMPLE 11 COMPARATIVE 3.0 2.30.48 0.30 Yes 92.5 EXAMPLE 12 COMPARATIVE 1.5 2.3 0.18 0.30 No 92.0EXAMPLE 13 Content Petroleum resin and Content Stretching ratio (wt. %)terpene resin (wt. %) (longitudinal × transverse) COMPARATIVE 100 — — 5× 10 EXAMPLE 1 COMPARATIVE 100 — — 7 × — EXAMPLE 2 COMPARATIVE 100 — — (5 × 13) EXAMPLE 3 COMPARATIVE 100 — — 5 × — EXAMPLE 4 COMPARATIVE 97hydrogenated  3 5 × 9 EXAMPLE 5 dicyclopentadiene COMPARATIVE 97hydrogenated  3 (7 × 8) EXAMPLE 6 dicyclopentadiene COMPARATIVE 97hydrogenated  3 8 × — EXAMPLE 7 dicyclopentadiene COMPARATIVE 90hydrogenated 10 5 × 9 EXAMPLE 8 dicyclopentadiene COMPARATIVE 90hydrogenated 10 (8 × 7) EXAMPLE 9 dicyclopentadiene COMPARATIVE 90hydrogenated 10 9 × — EXAMPLE 10 dicyclopentadiene COMPARATIVE 100 — — 5 × 12 EXAMPLE 11 COMPARATIVE 95 unhydrogenated gum  5  5 × 11 EXAMPLE12 rosin COMPARATIVE 100 — — 8 × — EXAMPLE 13

TABLE 4 Young's Young's modulus modulus F2 value F5 value (longitudinal)(transverse) m value at (longitudinal) (longitudinal) at 25° C. at 25°C. 25° C. at 25° C. at 25° C. (GPa) (GPa) (−) (MPa) (MPa) COMPARATIVE1.8 3.7 0.33 33 40 EXAMPLE 1 COMPARATIVE — — — — — EXAMPLE 2 COMPARATIVE— — — — — EXAMPLE 3 COMPARATIVE — — — — — EXAMPLE 4 COMPARATIVE 2.1 4.00.34 38 47 EXAMPLE 5 COMPARATIVE — — — — — EXAMPLE 6 COMPARATIVE — — — —— EXAMPLE 7 COMPARATIVE 2.6 4.5 0.37 42 51 EXAMPLE 8 COMPARATIVE — — — —— EXAMPLE 9 COMPARATIVE — — — — — EXAMPLE 10 COMPARATIVE 1.7 2.1 0.45 4150 EXAMPLE 11 COMPARATIVE 1.9 4.2 0.31 37 44 EXAMPLE 12 COMPARATIVE 2.71.1 0.71 43 97 EXAMPLE 13 Young's Young's modulus (longitudinal) atmodulus (transverse) at 80° C. (GPa) 80° C. (GPa) m value at 80° C. (−)COMPARATIVE 0.30 0.60 0.33 EXAMPLE 1 COMPARATIVE — — — EXAMPLE 2COMPARATIVE — — — EXAMPLE 3 COMPARATIVE — — — EXAMPLE 4 COMPARATIVE 0.250.55 0.31 EXAMPLE 5 COMPARATIVE — — — EXAMPLE 6 COMPARATIVE — — —EXAMPLE 7 COMPARATIVE 0.30 0.45 0.40 EXAMPLE 8 COMPARATIVE — — — EXAMPLE9 COMPARATIVE — — — EXAMPLE 10 COMPARATIVE 0.21 0.25 0.46 EXAMPLE 11COMPARATIVE 0.25 0.55 0.31 EXAMPLE 12 COMPARATIVE 0.40 0.15 0.73 EXAMPLE13 Heat Heat shrinkage shrinkage Water Vapor (longitudinal) at(transverse) Sum of heat permeability 120° C. at 120° C. shrinkage at(g/m²/d/ Converting (%) (%) 120° C. 0.1 mm) ability COMPARATIVE 4.0 2.06.0 1.6 Poor EXAMPLE 1 COMPARATIVE — — — — — EXAMPLE 2 COMPARATIVE — — —— — EXAMPLE 3 COMPARATIVE — — — — — EXAMPLE 4 COMPARATIVE 3.8 1.2 5.01.3 Poor EXAMPLE 5 COMPARATIVE — — — — — EXAMPLE 6 COMPARATIVE — — — — —EXAMPLE 7 COMPARATIVE 4.0 1.5 5.5 0.9 Poor EXAMPLE 8 COMPARATIVE — — — —— EXAMPLE 9 COMPARATIVE — — — — — EXAMPLE 10 COMPARATIVE 1.5 0.5 2.0 2.2Poor EXAMPLE 11 COMPARATIVE 3.1 1.7 4.8 2.0 Poor EXAMPLE 12 COMPARATIVE4.0 −0.5   3.5 1.8 Poor EXAMPLE 13

Tables 1 to 4 demonstrate that, since the biaxially stretchedpolypropylene film comprises a polypropylene which comprises apolypropylene having a melt strength (MS) and a melt flow rate (MFR)measured at 230° C. that satisfy formula (1), or a polypropylene whichconsists of a polypropylene satisfying the formula (2) between the meltstrength (MS) and the melt flow rate (MFR), and at least one additivethat has compatibility with the polypropylene and can provide plasticityduring stretching, a film having a high tension resistance and superiordimensional stability and moisture-proof property can be prepared.Moreover, such a superior quality film can be stably manufacturedwithout process failures such as film breakages by using a conventionallongitudinal-transverse sequential biaxial stretching machine.

Example 16

To 90 percent by weight of a polypropylene prepared by blending apublicly known polypropylene having a Trouton ratio of 12, a meso pentadfraction (mmmm) of 92%, an isotactic index (II) of 96%, a melt strength(MS) of 1.5 cN, and a melt flow rate (MFR) of 2.3 g/10 min with 5percent by weight of a high-melt-strength polypropylene (HMS-PP) havinga Trouton ratio of 50, a meso pentad fraction (mmmm) of 92%, anisotactic index (II) of 96.5%, a melt strength of 20 cN, and a melt flowrate of 3 g/10 min and containing long-chain branches, 10 percent byweight of polydicyclopentadiene having Tg of 80° C., a bromine number of3 cg/g, and a hydrogenation rate of 99%, which is a petroleum resinsubstantially containing no polar-group, was added as an additive thathas compatibility with the polypropylene and can provide plasticityduring stretching to prepare a resin. To 100 parts by weight of thisresin, 0.15 part by weight of crosslinked particles of apolymethacrylicacid-based polymer (crosslinked PMMA) having an averageparticle size of 2 μm was added as crosslinked organic particles, and0.8 parts by weight of a 1:1 mixture of glycerin fatty acid ester andalkyldiethanolamine fatty acid ester was added as an antistatic agent.The resulting mixture was fed into a twin-screw extruder, was extrudedat 240° C. into a gut-shape, cooled in a 20° C. water bath, and cut intoa 3-mm length by a chip cutter. The resulting chips were dried for 2hours at 100° C., fed into a single-screw extruder, melted at 260° C.,and filtered. The resulting filtered material was extruded from a slitdie and formed into a sheet by winding on a metal drum having atemperature of 25° C.

This sheet was passed between rolls maintained at 135° C., andpre-heated, and passed between rolls, which had different rotating speedand were maintained at 140° C., so that the sheet is stretched to 9times the initial length in the longitudinal direction. The stretchedsheet was then immediately cooled to room temperature. The stretchedfilm was next fed into a tenter to be pre-heated at 165° C., stretchedin the transverse direction to 7 times the initial length at 160° C.,and heat-set at 160° C. while being relaxed in the transverse directionby 8%. The film was then cooled and wound so as to obtain a biaxiallystretched polypropylene film having a thickness of 15 μm.

The composition of the raw material and the results of the evaluation ofthe film characteristics are shown in Tables 5 and 6. The resulting filmhad a high Young's modulus in the longitudinal direction and superiortension resistance, dimensional stability, moisture-proof property, andconverting ability.

Example 17

A biaxially stretched polypropylene film of EXAMPLE 17 having athickness of 15 μm was prepared as in EXAMPLE 16 except that thestretching ratio in the longitudinal direction was increased to 11.

The results are shown in Tables 5 and 6. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 18

A biaxially stretched polypropylene film of EXAMPLE 18 having athickness of 15 μm was prepared as in EXAMPLE 1 except that 3 percent byweight of β-pinene having a Tg of 75° C., a bromine number of 4 cg/g,and a hydrogenation rate of 99%, which is a terpene resin substantiallycontaining no polar-group, was added as an additive that hascompatibility with the polypropylene and can provide plasticity duringstretching, and that the film is stretched to 8 times the initial lengthin the longitudinal direction and to 8 times the initial length in thetransverse direction.

The results are shown in Tables 5 and 6. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 19

A biaxially stretched polypropylene film of EXAMPLE 19 having athickness of 15 μm was prepared as in EXAMPLE 18 except that 8 percentby weight of the additive terpene resin was added.

The results are shown in Tables 5 and 6. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 20

A biaxially stretched polypropylene film of EXAMPLE 20 having athickness of 15 μm was prepared as in EXAMPLE 16 except that 10 percentby weight of the HMS-PP containing long-chain branches was blended, andthat 5 percent by weight of polydicyclopentadiene was added. Moreover,the film was stretched to 9 times the initial length in the longitudinaldirection and to 7 times the initial length in the transverse direction.

The results are shown in Tables 5 and 6. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 21

To 85 percent by weight of a HMS-PP having a Trouton ratio of 50, a mesopentad fraction (mmmm) of 97%, an isotactic index (II) of 96.5%, a meltstrength (MS) of 20 cN, and a melt flow rate (MFR) of 3 g/10 min andcontaining long-chain branches, 15 percent by weight of a mixturecontaining β-pinene having a Tg of 75° C., a bromine number of 4 cg/g,and a hydrogenation rate of 99%, and hydrogenated β-dipentene having aTg of 75° C., a bromine number of 3 cg/g, and a hydrogenation rate of99%, which is a terpene resins substantially containing no polar-groupswas added as an additive that has compatibility with the polypropyleneand can provide plasticity during stretching to prepare a resin. To 100parts by weight of this resin, 0.15 parts by weight of crosslinkedparticles of a polystyrene-based polymer (crosslinked PS) having anaverage particle size of 1 μm was added as crosslinked organicparticles, and 0.8 parts by weight of a 1:1 mixture of glycerin fattyacid ester and alkyldiethanolamine fatty acid ester was added as anantistatic agent. The resulting mixture was fed into a twin-screwextruder, was extruded at 240° C. into a gut-shape, cooled in a 20° C.water bath, and cut into a 3-mm length by a chip cutter. The resultingchips were dried for 2 hours at 100° C., fed into a single-screwextruder, melted at 260° C., and filtered. The resulting filteredmaterial was extruded from a slit die and formed into a sheet by windingon a metal drum having a temperature of 30° C.

This sheet was passed between rolls maintained at 132° C., andpre-heated, and passed between rolls, which had different rotating speedand were maintained at 137° C. so that the sheet is stretched to 8 timesthe initial length in the longitudinal direction. The stretched sheetwas then immediately cooled to room temperature. The stretched film wasnext fed into a tenter to be pre-heated at 165° C., stretched in thetransverse direction to 8 times the initial length at 160° C., andheat-set at 160° C. while being relaxed in the transverse direction by8%. The film was then cooled and wound so as to obtain a biaxiallystretched polypropylene film having a thickness of 15 μm.

The results are shown in Tables 5 and 6. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 22

A biaxially stretched polypropylene film of EXAMPLE 22 having athickness of 15 μm was prepared as in EXAMPLE 21 except that, to 80percent by weight of a polypropylene prepared by blending a publiclyknown polypropylene having a Trouton ratio of 12, a meso pentad fraction(mmmm) of 92%, an isotactic index (II) of 96%, a melt strength (MS) of1.5 cN, and a melt flow rate (MFR) of 2.3 g/10 min with 5 percent byweight of a HMS-PP having a Trouton ratio of 50, a meso pentad fraction(mmmm) of 97%, an isotactic index (II) of 96.5%, a melt strength of (MS)20 cN, and a melt flow rate (MFR) of 3 g/10 min and containinglong-chain branches, 20 percent by weight of polydicyclopentadienehaving Tg of 80° C., a bromine number of 3 cg/g, and a hydrogenationrate of 99%, which is a petroleum resin substantially containing nopolar-group, was added as an additive that has compatibility with thepolypropylene and can provide plasticity during stretching. Moreover,the film was stretched to 11 times the initial length in thelongitudinal direction and 6 times the initial length in the transversedirection.

The results are shown in Tables 5 and 6. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 23

A biaxially stretched polypropylene film of EXAMPLE 23 having athickness of 15 μm was prepared as in EXAMPLE 18, except that apolypropylene prepared by blending 15 percent by weight of a HMS-PPhaving a Trouton ratio of 40, a meso pentad fraction (mmmm) of 95%, anisotactic index (II) of 96%, a melt strength (MS) of 15 cN, and a meltflow rate (MFR) of 2.0 g/10 min and containing long-chain branches wasused.

The results are shown in Tables 5 and 6. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 24

A biaxially stretched polypropylene film of EXAMPLE 24 having athickness of 15 μm was prepared as in EXAMPLE 23 except that 10 percentby weight of the HMS-PP was blended.

The results are shown in Tables 5 and 6. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 25

A biaxially stretched polypropylene film of EXAMPLE 25 having athickness of 15 μm was prepared as in EXAMPLE 18, except that 5 percentby weight of a HMS-PP having a Trouton ratio of 60, a meso pentadfraction (mmmm) of 94%, an isotactic index (II) of 95.5%, a meltstrength (MS) of 30 cN, and a melt flow rate (MFR) of 2.1 g/10 min andcontaining long-chain branches was blended.

The results are shown in Tables 5 and 6. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 26

A biaxially stretched polypropylene film of EXAMPLE 26 having athickness of 15 μm was prepared as in EXAMPLE 16, except that 30 percentby weight of the HMS-PP containing long-chain branches was blended.Moreover, the film was stretched to 10 times the initial length in thelongitudinal direction and to 7 times the initial length in thetransverse direction.

The results are shown in Tables 5 and 6. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 27

A biaxially stretched polypropylene film of EXAMPLE 28 having athickness of 15 μm was prepared as in EXAMPLE 16, except that apolypropylene prepared by blending a publicly known polypropylene havinga Trouton ratio of 10, a meso pentad fraction (mmmm) of 98%, anisotactic index (II) of 99%, a melt strength (MS) of 1 cN, and a meltflow rate (MFR) of 3.1 g/10 min with 5 percent by weight of the HMS-PPwas used. Moreover, the film was stretched to 10 times in thelongitudinal direction and to 8 times the initial length in thetransverse direction.

The results are shown in Tables 5 and 6. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 28

A biaxially stretched polypropylene film of EXAMPLE 28 having athickness of 15 μm was prepared as in EXAMPLE 20, except that apolypropylene prepared by blending a publicly known polypropylene havinga Trouton ratio of 11, a meso pentad fraction (mmmm) of 95.5%, anisotactic index (II) of 96%, a melt strength (MS) of 1.3 cN, and a meltflow rate (MFR) of 2.5 g/10 min with 10 percent by weight of the HMS-PPwas blended. Moreover, the film was stretched to 9 times the initiallength in the longitudinal direction and to 8 times the initial lengthin the transverse direction.

The results are shown in Tables 5 and 6. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 29

A biaxially stretched polypropylene film of COMPARABLE EXAMPLE 29 havinga thickness of 15 μm was prepared as in EXAMPLE 19 except thatstretching in the longitudinal direction was performed in two steps,i.e., the film was preheated at 135° C., stretched to 1.5 times theinitial length at 137° C. in the first step, and stretched to 5.3 timesthe initial length at 142° C. in the second step.

The results are shown in Tables 5 and 6. The resulting film had a highYoung's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

TABLE 5 Characteristics of polypropylene resin Characteristics of HMS-PPresin Trouton Content Trouton ratio of Meso pentad fraction of PP ratio(wt. %) PP as a whole as a whole (%) EXAMPLE 16 50 5 22 92.3 EXAMPLE 1750 5 22 92.3 EXAMPLE 18 50 5 22 92.3 EXAMPLE 19 50 5 22 92.3 EXAMPLE 2050 10 26 92.5 EXAMPLE 21 50 100 50 97.0 EXAMPLE 22 50 5 22 92.3 EXAMPLE23 40 15 18 92.5 EXAMPLE 24 40 10 13 92.3 EXAMPLE 25 60 5 30 92.1EXAMPLE 26 50 30 36 93.5 EXAMPLE 27 50 5 19 98.0 EXAMPLE 28 50 10 2595.6 EXAMPLE 29 50 5 22 92.3 Content Petroleum resin and terpene ContentStretching ratio (wt. %) resin (wt. %) (longitudinal × transverse)EXAMPLE 16 90 hydrogenated 10 9 × 7 dicyclopentadiene EXAMPLE 17 90hydrogenated 10 11 × 6  dicyclopentadiene EXAMPLE 18 97 hydrogenatedβ-pinene 3 8 × 8 EXAMPLE 19 92 hydrogenated β-pinene 8 8 × 8 EXAMPLE 2095 hydrogenated 5 9 × 7 dicyclopentadiene EXAMPLE 21 85 hydrogenatedβ-pinene and 15 8 × 8 hydrogenated β-dipentene EXAMPLE 22 80hydrogenated 20 11 × 6  dicyclopentadiene EXAMPLE 23 97 hydrogenatedβ-pinene 3 8 × 8 EXAMPLE 24 97 hydrogenated β-pinene 3 8 × 8 EXAMPLE 2597 hydrogenated β-pinene 3 8 × 8 EXAMPLE 26 90 hydrogenated 10 10 × 7 dicyclopentadiene EXAMPLE 27 90 hydrogenated 10 10 × 8 dicyclopentadiene EXAMPLE 28 hydrogenated 5 9 × 8 dicyclopentadieneEXAMPLE 29 92 hydrogenated β-pinene 8 (1.5 * 5.3) × 9

TABLE 6 Young's Young's modulus modulus F2 value F5 value (longitudinal)(transverse) at m value at (longitudinal) (longitudinal) at 25° C. 25°C. 25° C. at 25° C. at 25° C. (GPa) (GPa) (−) (MPa) (MPa) EXAMPLE 16 3.93.8 0.51 67 95 EXAMPLE 17 4.4 3.4 0.56 75 110 EXAMPLE 18 3.1 4.0 0.44 4862 EXAMPLE 19 3.8 3.9 0.49 63 81 EXAMPLE 20 3.3 3.4 0.49 53 78 EXAMPLE21 3.8 3.9 0.49 69 92 EXAMPLE 22 5.0 3.2 0.61 76 115 EXAMPLE 23 2.9 4.00.42 46 58 EXAMPLE 24 2.7 4.3 0.39 42 54 EXAMPLE 25 3.4 3.6 0.49 51 73EXAMPLE 26 4.2 3.1 0.58 69 101 EXAMPLE 27 4.0 4.2 0.49 70 90 EXAMPLE 283.5 4.3 0.45 58 68 EXAMPLE 29 4.2 4.4 0.49 65 94 Young's modulus Young'smodulus (transverse) at 80° C. (longitudinal) at 80° C. (GPa) (GPa) mvalue at 80° C. (−) EXAMPLE 16 0.62 0.62 0.50 EXAMPLE 17 0.67 0.60 0.53EXAMPLE 18 0.50 0.55 0.48 EXAMPLE 19 0.63 0.63 0.50 EXAMPLE20 0.53 0.530.50 EXAMPLE 21 0.59 0.59 0.50 EXAMPLE 22 0.78 0.65 0.55 EXAMPLE 23 0.480.60 0.44 EXAMPLE 24 0.43 0.58 0.43 EXAMPLE 25 0.55 0.55 0.50 EXAMPLE 260.67 0.63 0.52 EXAMPLE 27 0.75 0.75 0.50 EXAMPLE 28 0.68 0.76 0.47EXAMPLE 29 0.62 0.65 0.49 Heat Heat shrinkage shrinkage (longitudinal)(transverse) Sum of heat Water vapor at 120° C. at 120° C. shrinkage atpermeability Converting (%) (%) 120° C. (g/m²/d/0.1 mm) ability EXAMPLE16 3.7 1.1 4.8 0.7 Good EXAMPLE 17 4.3 1.1 5.4 0.6 Good EXAMPLE 18 2.81.0 3.8 1.2 Good EXAMPLE 19 3.0 1.1 4.1 0.9 Good EXAMPLE20 3.2 1.0 4.21.1 Good EXAMPLE 21 3.2 1.6 4.8 0.7 Good EXAMPLE 22 4.0 1.3 5.3 0.5 GoodEXAMPLE 23 2.8 1.0 3.8 1.2 Good EXAMPLE 24 3.0 1.1 4.1 1.2 Good EXAMPLE25 2.7 0.8 3.5 1.2 Good EXAMPLE 26 3.3 1.2 4.5 0.7 Good EXAMPLE 27 1.90.6 2.5 0.5 Good EXAMPLE 28 1.5 0.0 1.5 0.7 Good EXAMPLE 29 4.0 1.5 5.50.9 Good

Comparative Examples 1 to 4, and 11 to 13

The films of COMPARATIVE EXAMPLE 1 to 4, and 11 to 13 are shown inTables 7 and 8.

Comparative Example 14

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 14having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 1except that 3 percent by weight of β-pinene having a Tg of 75° C., abromine number of 4 cg/g, and a hydrogenation rate of 99%, which is aterpene resin substantially containing no polar-group, as an additivethat has compatibility with the polypropylene and can provide plasticityduring stretching, was added to 97 percent by weight of polypropylene,and that the film was stretched to 5 times the initial length in thelongitudinal direction and to 9 times the initial length in thetransverse direction.

The results are shown in Tables 7 and 8. The resulting film had lowYoung's modulus in the longitudinal direction, insufficient tensionresistance, and poor converting ability.

Comparative Example 15

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 15having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 14except that the film was stretched to 7 times the initial length in thelongitudinal direction and to 8 times the initial length in thetransverse direction.

The results are shown in Tables 7 and 8. Because film breakage occurredduring transverse stretching, a film having a sufficient length couldnot be obtained. The resulting film was not suited for industrialproduction.

Comparative Example 16

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 16having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 14except that the stretching ratio in the longitudinal direction wasincreased to 8.

The results are shown in Tables 7 and 8. Because significant degree offilm breakage occurred during transverse stretching, a sufficient filmcould not be obtained.

Comparative Example 17

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 17having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 14except that 10 percent by weight of β-pinene was added.

The results are shown in Tables 7 and 8. The film had a low Young'smodulus in the longitudinal direction at 80° C., insufficient tensionresistance, and poor dimensional stability and converting ability.

Comparative Example 18

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 18having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 17except that the film was stretched to 8 times the initial length in thelongitudinal direction and to 7 times the initial length in thetransverse direction.

The results are shown in Tables 7 and 8. Because film breakage occurredduring transverse stretching, a film having a sufficient length couldnot be obtained. The resulting film was not suited for industrialproduction.

Comparative Example 19

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 19having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 17except that the stretching ratio in the longitudinal direction wasincreased to 9.

The results are shown in Tables 7 and 8. Because significant degree offilm breakage occurred during transverse stretching, a sufficient filmcould not be obtained.

TABLE 7 Characteristics of polypropylene resin Characteristics of HMS-PPresin Meso pentad fraction of Trouton Content Trouton ratio of PP as awhole ratio (wt. %) PP as a whole (%) COMPARATIVE — — 12 92.0 EXAMPLE 1COMPARATIVE — — 12 92.0 EXAMPLE 2 COMPARATIVE — — 10 97.5 EXAMPLE 3COMPARATIVE — — 8 99.8 EXAMPLE 4 COMPARATIVE 50 100 50 97.0 EXAMPLE 11COMPARATIVE 50  10 26 92.5 EXAMPLE 12 COMPARATIVE — — 12 92.0 EXAMPLE 13COMPARATIVE — — 12 92.0 EXAMPLE 14 COMPARATIVE — — 12 92.0 EXAMPLE 15COMPARATIVE — — 12 92.0 EXAMPLE 16 COMPARATIVE — — 12 92.0 EXAMPLE 17COMPARATIVE — — 12 92.0 EXAMPLE 18 COMPARATIVE — — 12 92.0 EXAMPLE 19Content Petroleum resin Content Stretching ratio (wt. %) and terpeneresin (wt. %) (longitudinal × transverse) COMPARATIVE 100 — —  5 × 10EXAMPLE 1 COMPARATIVE 100 — — 7 × — EXAMPLE 2 COMPARATIVE 100 — —  (5 ×13) EXAMPLE 3 COMPARATIVE 100 — — 5 × — EXAMPLE 4 COMPARATIVE 100 — —  5× 12 EXAMPLE 11 COMPARATIVE 95 unhydrogenated 5  5 × 11 EXAMPLE 12 gumrosin COMPARATIVE 100 — — 8 × — EXAMPLE 13 COMPARATIVE 97 hydrogenated 35 × 9 EXAMPLE 14 β-pinene COMPARATIVE 97 hydrogenated 3 (7 × 8) EXAMPLE15 β-pinene COMPARATIVE 97 hydrogenated 3 8 × — EXAMPLE 16 β-pineneCOMPARATIVE 90 hydrogenated 10 5 × 9 EXAMPLE 17 β-pinene COMPARATIVE 90hydrogenated 10 (8 × 7) EXAMPLE 18 β-pinene COMPARATIVE 90 hydrogenated10 9 × — EXAMPLE 19 β-pinene

TABLE 8 Young's Young's modulus modulus F2 value F5 value (longitudinal)(transverse) m value at (longitudinal) (longitudinal) at 25° C. at 25°C. 25° C. at 25° C. at 25° C. (GPa) (GPa) (−) (MPa) (MPa) COMPARATIVE1.8 3.7 0.33 33 40 EXAMPLE 1 COMPARATIVE — — — — — EXAMPLE 2 COMPARATIVE— — — — — EXAMPLE 3 COMPARATIVE — — — — — EXAMPLE 4 COMPARATIVE 1.7 2.10.45 41 50 EXAMPLE 11 COMPARATIVE 1.9 4.2 0.31 37 44 EXAMPLE 12COMPARATIVE 2.7 1.1 0.71 43 97 EXAMPLE 13 COMPARATIVE 2.1 4.0 0.34 38 45EXAMPLE 14 COMPARATIVE — — — — — EXAMPLE 15 COMPARATIVE — — — — —EXAMPLE 16 COMPARATIVE 2.4 4.7 0.34 40 49 EXAMPLE 17 COMPARATIVE — — — —— EXAMPLE 18 COMPARATIVE — — — — — EXAMPLE 19 Young's modulus Young'smodulus (longitudinal) at 80° C. (transverse) at 80° C. (GPa) (GPa) mvalue at 80° C. (−) COMPARATIVE 0.30 0.60 0.33 EXAMPLE 1 COMPARATIVE — —— EXAMPLE 2 COMPARATIVE — — — EXAMPLE 3 COMPARATIVE — — — EXAMPLE 4COMPARATIVE 0.21 0.25 0.46 EXAMPLE 11 COMPARATIVE 0.25 0.55 0.31 EXAMPLE12 COMPARATIVE 0.40 0.15 0.73 EXAMPLE 13 COMPARATIVE 0.28 0.55 0.34EXAMPLE 14 COMPARATIVE — — — EXAMPLE 15 COMPARATIVE — — — EXAMPLE 16COMPARATIVE 0.28 0.50 0.36 EXAMPLE 17 COMPARATIVE — — — EXAMPLE 18COMPARATIVE — — — EXAMPLE 19 Heat Heat Sum of shrinkage shrinkage heat(longitudinal) (transverse) shrinkage Water vapor at 120° C. at 120° C.at permeability Converting (%) (%) 120° C. (g/m²/d/0.1 mm) abilityCOMPARATIVE 4.0 2.0 6.0 1.6 Poor EXAMPLE 1 COMPARATIVE — — — — — EXAMPLE2 COMPARATIVE — — — — — EXAMPLE 3 COMPARATIVE — — — — — EXAMPLE 4COMPARATIVE 1.5 0.5 2.0 2.2 Poor EXAMPLE 11 COMPARATIVE 3.1 1.7 4.8 2.0Poor EXAMPLE 12 COMPARATIVE 4.0 −0.5   3.5 1.8 Poor EXAMPLE 13COMPARATIVE 4.0 1.0 5.0 1.4 Poor EXAMPLE 14 COMPARATIVE — — — — —EXAMPLE 15 COMPARATIVE — — — — — EXAMPLE 16 COMPARATIVE 4.2 1.8 6.0 1.0Poor EXAMPLE 17 COMPARATIVE — — — — — EXAMPLE 18 COMPARATIVE — — — — —EXAMPLE 19

Tables 5 to 8 demonstrate that, since the biaxially stretchedpolypropylene film comprises a polypropylene which comprises apolypropylene having a Trouton ratio of 30 or more or a polypropylenewhich consists of a polypropylene having a Trouton ratio of 16 or more,and at least one additive that has compatibility with the polypropyleneand can provide plasticity during stretching, a film having a hightension resistance and superior dimensional stability and moisture-proofproperty can be prepared. Moreover, such a superior quality film can bestably manufactured without process failures such as film breakages byusing a conventional longitudinal-transverse sequential biaxialstretching machine.

Example 30

A biaxially stretched polypropylene film of EXAMPLE 30 having athickness of 15 μm was prepared as in EXAMPLE 3 except that thetemperature of the cooling drum was increased to 80° C. to prepare theunstretched sheet. The results of evaluation of the film characteristicsare shown in Table 9.

Comparative Example 20

A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 20having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 1except that the temperature of the cooling drum was increased to 80° C.to prepare the unstretched sheet. The results of evaluation of the filmcharacteristics are shown in Table 9.

TABLE 9 Young's Young's modulus modulus F2 value F5 value (longitudinal)(transverse) m value at (longitudinal) (longitudinal) at 25° C. at 25°C. 25° C. at 25° C. at 25° C. (GPa) (GPa) (−) (MPa) (MPa) EXAMPLE 30 4.03.5 0.53 63 88 COMPARATIVE 1.9 3.9 0.33 33 41 EXAMPLE 20 Young's modulusYoung's modulus (longitudinal) at 80° C. (transverse) at 80° C. (GPa)(GPa) m value at 80° C. (−) EXAMPLE 30 0.70 0.50 0.58 COMPARATIVE 0.300.60 0.33 EXAMPLE 20 Heat Heat Sum of shrinkage shrinkage heat(longitudinal) (transverse) shrinkage Water vapor at 120° C. at 120° C.at 120° C. permeability Converting (%) (%) (%) (g/m²/d/0.1 mm) abilityEXAMPLE 30 2.7 0.3 3.0 1.0 Good COMPARATIVE 3.9 1.8 5.7 1.6 Poor EXAMPLE20Observation Results of Fibril Structures of Examples 1, 3, 17, 19, and30, and Comparative Examples 1, 5, 17 and 20

The fibril structure of each of the films of EXAMPLES 1, 3, 17, 19, and30, and COMPARATIVE EXAMPLES 1, 5, 17 and 20 described above wasobserved by using an atomic force microscope (AFM).

The observation results of the fibril structures are shown in Table 10.The films contained longitudinal fibrils that rarely deform againstapplied stresses, resulting in a film having a superior tensionresistance. Moreover, the handling convenience during converting processwas also superior because the formula below between Young's modulus inthe longitudinal direction Y(MD) at 25° C. and the heat shrinkage in thelongitudinal direction S(MD) at 120° C. was satisfied:Y(MD)≧S(MD)−1.

Accordingly, a film having such superior characteristics can be stablymanufactured. Moreover, the number of the fibrils and the width of thefibrils were controllable by adjusting the film-forming conditions suchas the temperature of the cooling drum. In contrast, conventional filmsof the COMPARATIVE EXAMPLES did not contain longitudinal fibrils, andthe fibril structures readily deformed against applied stresses,resulting in a film having low tension resistance and, because the filmsdid not satisfy the above-described formula, exhibited poor convertingability. Furthermore, no longitudinal fibrils were obtained even whenthe film-forming conditions were altered.

TABLE 10 Average Presence of width of No. of longitudinal longitudinallongitudinal formula fibrils fibrils fibrils (5) EXAMPLE 1 A 75 3Satisfied EXAMPLE 3 C 59 2 Satisfied EXAMPLE 17 A 120 5 SatisfiedEXAMPLE 19 B 70 2 Satisfied EXAMPLE 30 A 72 3 Satisfied COMPARATIVE NONE— — Not EXAMPLE 1 satisfied COMPARATIVE NONE — — Not EXAMPLE 5 satisfiedCOMPARATIVE NONE — — Not EXAMPLE 17 satisfied COMPARATIVE NONE — — NotEXAMPLE 20 satisfied

Example 31

A biaxially stretched polypropylene film was prepared by biaxialstretching as in EXAMPLE 3 except that the antistatic agent was notadded and that the amount of the crosslinked particles of apolymethacrylicacid-based copolymer (crosslinked PMMA) having an averageparticle size of 2μm was changed to 0.05 parts by weight. Subsequently,one side of the film was subjected to corona discharge treatment in anatmosphere containing 15% of carbon dioxide gas and 85% of nitrogen gasto obtain a biaxially stretched polypropylene film with a surfacewetting tension of 45 mN/m. The biaxially stretched polypropylene filmwas then installed in a vacuum metallization apparatus. While the filmwas allowed to run, aluminum metal was heated, melted, and evaporated sothat a layer having a thickness of 30 nm was deposited on the side thathad been subjected to corona discharge treatment. Thus, a metallizedbiaxially stretched polypropylene film was obtained.

The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 200ml/m².d.MPa; and water vapor permeability: 0.2 g/m².d. The gas barrierproperty after converting process was as follows: oxygen permeability:205 ml/m².d.MPa; and water vapor permeability: 0.2 g/m².d. Nosignificant change in gas barrier properties was observed.

Example 32

A biaxially stretched polypropylene film was prepared as in EXAMPLE 5,except that the antistatic agent and the crosslinked PMMA particles werenot added and that 0.05 parts by weight of crosslinked silicon particleshaving an average particle size of 2 μm were added. Then metallizedbiaxially stretched polypropylene film was prepared as in EXAMPLE 31.

The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 150ml/m².d.MPa; and water vapor permeability: 0.15 g/m².d. The gas barrierproperties, i.e., the oxygen permeability and the water vaporpermeability, after converting process were the same as those beforeconverting.

Example 33

A biaxially stretched polypropylene film was prepared as in EXAMPLE 16,except that the antistatic agent was not added and that 0.02 parts byweight of crosslinked PMMA particles having an average particle size of2 μm were added. Then metallized biaxially stretched polypropylene filmwas prepared as in EXAMPLE 31.

The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 130ml/m².d.MPa; and water vapor permeability: 0.13 g/m².d.MPa. The gasbarrier properties, i.e., the oxygen permeability and the water vaporpermeability, after converting process were the same as those beforeconverting.

Example 34

In EXAMPLE 26, a metallized biaxially stretched polypropylene film wasprepared as in EXAMPLE 33.

The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 100ml/m².d.MPa; and water vapor permeability: 0.1 g/m².d. The gas barrierproperties, i.e., the oxygen permeability and the water vaporpermeability, after converting process were the same as those beforeconverting.

Comparative Example 21

A biaxially stretched polypropylene film was prepared as in COMPARATIVEEXAMPLE 1 except that the antistatic agent was not added and that theamount of the crosslinked particles of a polymethacrylicacid-basedcopolymer (crosslinked PMMA) having an average particle size of 2 μm waschanged to 0.05 part by weight as in EXAMPLE 31. Using this film, ametallized biaxially stretched polypropylene film was obtained as inEXAMPLE 31.

The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 300ml/m².d.MPa; and water vapor permeability: 0.25 g/m².d. The metallizedbiaxially stretched polypropylene film had low Young's modulus in thelongitudinal direction, insufficient tension resistance, and poorconverting ability. The gas barrier properties after converting processwere as follows: oxygen permeability: 620 ml/m².d.MPa; and water vaporpermeability: 0.23 g/m².d. The oxygen permeability dramatically degradedafter converting.

Comparative Example 22

In COMPARATIVE EXAMPLE 8, a metallized biaxially stretched polypropylenefilm was prepared as in EXAMPLE 31. The gas barrier properties of themetallized biaxially stretched polypropylene film were as follows:oxygen permeability: 270 ml/m².d.MPa; and water vapor permeability: 0.28g/m².d.

The metallized biaxially stretched polypropylene film had a low Young'smodulus at high temperature, i.e., 80° C., insufficient tensionresistance, and poor converting ability. The gas barrier propertiesafter converting process were as follows: oxygen permeability: 680ml/m².d.MPa; and water vapor permeability: 0.23 g/m².d. The oxygenpermeability dramatically degraded after converting.

Example 35

The resin composition as in EXAMPLE 3 but without the antistatic agentand with 0.05 part by weight of crosslinked particles of thepolymethacrylicacid-based polymer (crosslinked PMMA) was extruded andformed into a sheet as in EXAMPLE 3 to prepare a core layer. The sheetwas stretched in the longitudinal direction to 8 times the initiallength as in EXAMPLE 1, and the surface of the film stretched to 8 timeswas subjected to corona discharge treatment in air so as to obtain asurface wetting tension of 37 mN/m. A blended coating materialcontaining 100 parts by weight of “Hydran” AP-40F (manufactured byDainippon Ink and Chemicals, Inc., solid content: 30%) as awater-dispersible polyesterpolyurethane-based resin, 15 parts by weightof N-methylpyrrolidone as a water-soluble organic solvent, and 5 partsby weight of a melamine compound, i.e., “Beckamine” APM (manufactured byDainippon Ink and Chemicals, Inc.) as a crosslinking agent, and 2 partsby weight of a water-soluble acidic compound, i.e., “Catalyst” PTS(manufactured by Dainippon Ink and Chemicals, Inc.) as a crosslinkingaccelerator was applied on this treated surface by a coating bar to forma coating layer. Subsequently, the coated film was stretched in thetransverse direction as in EXAMPLES so as to prepare a biaxiallystretched polypropylene film. The film thickness construction wascoating layer/core layer=0.2 μm/15 μm. The adhesive strength between thesurface of the film of the present invention and the coating layer was2.3 N/cm, the centerline average roughness Ra of the coating layer was0.03 μm, and the surface gloss was 140%.

Next, the biaxially stretched polypropylene film was installed in avacuum metallizing apparatus, and aluminum metal was heated, melted, andevaporated so that the evaporated aluminum cohere and deposit on thefilm surface to make a metallization layer. Thus, a metallized biaxiallystretched polypropylene film was obtained.

The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 20 ml/m².d.MPa;and water vapor permeability: 0.07 g/m².d. The adhesive strength betweenthe coating layer and the metallization layer was 1.7 N/cm. The gasbarrier properties after converting process were maintained as high asthose before converting and were as follows: oxygen permeability 22ml/m².d.MPa; and water vapor permeability: 0.07 g/m².d.

Example 36

A biaxially stretched polypropylene film provided with a coating layerhaving a thickness of 0.2 μm was prepared as in EXAMPLE 35 except that ablended coating material containing 100 parts by weight of “Hydran”AP-40F (manufactured by Dainippon Ink and Chemicals, Inc., solidcontent: 30%) as a water-dispersible polyesterpolyurethane-based resin,5 parts by weight of a melamine compound, i.e., “Beckamine” APM(manufactured by Dainippon Ink and Chemicals, Inc.) as a crosslinkingagent, and 2 parts by weight of a water-soluble acidic compound, i.e.,“Catalyst” PTS (manufactured by Dainippon Ink and Chemicals, Inc.) as acrosslinking accelerator was coated using the coating bar. The adhesivestrength between the surface of the film and the coating layer was 2.0N/cm, the centerline average roughness Ra of the coating layer was 0.03μm, and the glossiness was 138%.

Next, an aluminum metallization layer was formed on the biaxiallystretched polypropylene film as in EXAMPLE 34 so as to obtain ametallized biaxially stretched polypropylene film.

The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 30 ml/m².d.MPa;and water vapor permeability: 0.08 g/m².d. The adhesive strength betweenthe coating layer and the metallization layer was 1.5 N/cm. The gasbarrier properties after converting process were maintained as high asthose before converting and were as follows: oxygen permeability 32ml/m².d.MPa; and water vapor permeability: 0.09 g/m².d.

Example 37

The surface of the biaxially stretched polypropylene film of EXAMPLE 16was subjected to corona discharge treatment in air so as to obtain asurface wetting tension of 37 mN/m, and the blended coating material ofEXAMPLE 34 was applied on this treated surface using an off-line gravurecoater to form a coating layer having a thickness of 0.2 μm. The filmwas wound and subjected to aluminum metallization as in EXAMPLE 35 toobtain a metallized biaxially stretched polypropylene film.

The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 10 ml/m².d.MPa;and water vapor permeability: 0.08 g/m².d. The adhesive strength betweenthe biaxially stretched polypropylene film and the coating layer was 3N/cm, and the adhesive strength between the coating layer and themetallization layer was 2 N/cm. The gas barrier properties afterconverting process were maintained as high as those before convertingand were as follows: oxygen permeability 12 ml/m².d.MPa; and water vaporpermeability: 0.08 g/m².d.

Example 38

A biaxially stretched polypropylene film was prepared as in EXAMPLE 26but without adding the antistatic agent and the particles and a coatinglayer was formed as in EXAMPLE 35. Subsequently, a metallized biaxiallystretched polypropylene film was prepared as in EXAMPLE 35.

The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 8 ml/m².d.MPa;and water vapor permeability: 0.05 g/m².d. The adhesive strength of thecoating layer was 3.2 N/cm, and the adhesive strength between thecoating layer and the metallization layer was 2.5 N/cm. The gas barrierproperties after converting process were maintained as high as thosebefore converting and were as follows: oxygen permeability 8ml/m².d.MPa; and water vapor permeability: 0.05 g/m².d.

Comparative Example 23

A metallized biaxially stretched polypropylene film was prepared as inEXAMPLE 35 but with a different coating material prepared as follows. Inthe presence of a catalyst, 0.12 mol of terephthalic acid, 0.84 mol ofisophthalic acid, 0.33 mol of diethylene glycol, and 0.65 mol ofneopentyl glycol were allowed to react at 190 to 220° C. for 6 hourswhile removing distillation water, and the resulting substance wassubjected to condensation reaction for 1 hour at 250° C. in vacuum so asto obtain a prepolymer. The prepolymer was blended with 0.13 mol of5-(2,5dioxotetrahydrofurfryl)-3-methyl-3-cyclohexene-1,2-dicarboxylanhydride so as to perform selective monoesterification reaction at 140°C. for 3 hours to obtain a polymer. Next, the polymer was neutralizedwith ammonia to prepare a polyester resin. To 100 parts by weight ofactive principle of the polyester resin, 10 parts by weight of anisocyanate compound, i.e., hexamethylene diisocyanate as a crosslinkingagent and 1.5 parts by weight of “Catalyst” PTS (manufactured byDainippon Ink and Chemicals, Inc.) as a crosslinking catalyst were addedto prepare the coating material.

The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 120ml/m².d.MPa; and water vapor permeability: 0.1 g/m².d. The adhesivestrength between the metallized biaxially stretched polypropylene filmand the coating layer was low, and coating layer peeled from the filmduring converting process. Thus, the gas barrier properties weredramatically decreased to an oxygen permeability of 750 ml/m².d.MPa anda water vapor permeability of 0.35 g/m².d.

Comparative Examples 24 and 25

A metallized biaxially stretched polypropylene film of COMPARATIVEEXAMPLE 24 was prepared as in EXAMPLE but with a coating layer having athickness of 0.03 μm. A metallized biaxially stretched polypropylenefilm of COMPARATIVE EXAMPLE 25 was prepared as in EXAMPLE 35 but with acoating layer having a thickness of 4 μm.

In COMPARATIVE EXAMPLE 24, gas barrier properties did not improve due tothe thin coating layer. The oxygen permeability was 195 ml/m².d.MPa, andthe water vapor permeability was 0.2 g/m².d.

In COMPARATIVE EXAMPLE 25, the coating layer did not sufficiently curedue to the large thickness of the layer, and the adhesive strength tothe film surface was low. As for the gas barrier properties, the oxygenpermeability was 210 ml/m².d.MPa, and the water vapor permeability was0.13 g/m².d.

Comparative Example 26

In COMPARATIVE EXAMPLE 1, a metallized biaxially stretched polypropylenefilm was prepared as in EXAMPLE 35.

Due to the deposition of the coating layer, the gas barrier propertiesof the metallized biaxially stretched polypropylene film were improved,i.e., oxygen permeability: 30 ml/m².d.MPa, and water vapor permeability:0.15 g/m².d. However, because the metallized biaxially stretchedpolypropylene film had a low Young's modulus in the longitudinaldirection and insufficient tension resistance, the gas barrierproperties significantly degraded after converting process, i.e., oxygenpermeability: 420 ml/m².d.MPa; and water vapor permeability: 0.27g/m².d.

Comparative Example 27

In COMPARATIVE EXAMPLE 14, a metallized biaxially stretchedpolypropylene film was prepared as in EXAMPLE 35. Due to the coatinglayer, the gas barrier properties of the metallized biaxially stretchedpolypropylene film were improved, i.e., oxygen permeability: 27ml/m².d.MPa, and water vapor permeability: 0.10 g/m².d. However, becausethe metallized biaxially stretched polypropylene film had a low Young'smodulus in the longitudinal direction and insufficient tensionresistance, the gas barrier properties significantly degraded afterconverting process, i.e., oxygen permeability: 370 ml/m².d.MPa; andwater vapor permeability: 0.23 /m².d.

TABLE 11 Thickness arrangement Adhesive Adhesive (μm) base Young'smodulus strength between strength of the layer/coating (longitudinal) atsurface and the metallization layer/metal- 25° C. coating layer layerlization layer (GPa) (N/cm) (N/cm) EXAMPLE 31 15/—/0.03 3.1 — 0.7EXAMPLE 32 15/—/0.03 3.6 — 0.6 EXAMPLE 33 15/—/0.03 3.9 — 0.7 EXAMPLE 3415/0.2/0.03 4.2 — 0.7 EXAMPLE 35 15/0.2/0.03 3.1 2.3 1.7 EXAMPLE 3615/0.2/0.03 3.1 2.0 1.5 EXAMPLE 37 15/0.2/0.03 3.9 3.0 2.0 EXAMPLE 3815/0.2/0.03 4.2 3.2 2.5 COMPARATIVE 15/—/0.03 2.0 — 0.7 EXAMPLE 21COMPARATIVE 15/—/0.03 2.6 — 0.7 EXAMPLE 22 COMPARATIVE 15/0.2/0.03 3.10.7 — EXAMPLE 23 COMPARATIVE 15/0.03/0.03 3.1 1.5 0.7 EXAMPLE 24COMPARATIVE 15/4/0.03 3.1 1.0 0.2 EXAMPLE 25 COMPARATIVE 15/0.2/0.03 2.02.3 1.7 EXAMPLE 26 COMPARATIVE 15/0.2/0.03 2.1 2.3 1.7 EXAMPLE 27 OxygenOxygen Water vapor permeability Water vapor permeability afterpermeability after after permeability after converting convertingmetallization metallization process process (ml/m²/d/MPa) (g/m²/d)(ml/m²/d/MPa) (g/m²/d) EXAMPLE 31 200 0.20 205 0.20 EXAMPLE 32 150 0.15150 0.15 EXAMPLE 33 130 0.13 130 0.13 EXAMPLE 34 100 0.10 100 0.10EXAMPLE 35 20 0.07 22 0.07 EXAMPLE 36 30 0.08 32 0.09 EXAMPLE 37 10 0.0812 0.08 EXAMPLE 38 8 0.05 8 0.05 COMPARATIVE 300 0.25 620 0.28 EXAMPLE21 COMPARATIVE 270 0.22 680 0.23 EXAMPLE 22 COMPARATIVE 120 0.10 7500.35 EXAMPLE 23 COMPARATIVE 195 0.20 200 0.20 EXAMPLE 24 COMPARATIVE 2100.30 220 0.23 EXAMPLE 25 COMPARATIVE 30 0.15 420 0.27 EXAMPLE 26COMPARATIVE 27 0.10 370 0.23 EXAMPLE 27

The results of the evaluation of the film characteristics are shown inTable 11. Because the biaxially stretched polypropylene film has highstiffness in the longitudinal direction, degradation in barrier propertyafter converting process can be avoided when the film is used as a basefilm of a metallized film. Moreover, by forming a coating layer betweenthe base layer and the metallization layer, the barrier property can befurther enhanced.

INDUSTRIAL APPLICABILITY

A biaxially stretched polypropylene film has an increased stiffness inthe longitudinal direction without degrading important characteristicssuch as dimensional stability and moisture-proof property, when comparedwith conventional biaxially stretched polypropylene films. Thus, thebiaxially stretched polypropylene film has superior handling convenienceand exhibits superior tension resistance against converting tensionapplied during film converting such as printing, laminating, coating,metallization, and bag-making. The troubles derived from the quality ofthe base film, such as cracks and print pitch displacement, can beavoided. Moreover, since the film has a stiffness in the longitudinaldirection higher than that of the conventional polypropylene film of thesame thickness and exhibits a superior tension resistance, sufficientconverting ability can be maintained with a thickness smaller than thatof conventional biaxially stretched polypropylene films.

The biaxially stretched polypropylene film is suitable for packaging andfor industrial use.

1. A biaxially stretched polypropylene film comprising a polypropylenewhich comprises a polypropylene having a melt strength (MS) and a meltflow rate (MFR) measured at 230° C. that satisfies formula (1) below:log(MS)>−0.61 log(MFR)+0.82  (1) and a petroleum resin substantiallycontaining no polar-group and/or a terpene resin substantiallycontaining no polar-group that has compatibility with the polypropyleneand provides plasticity during stretching, wherein the Young's modulusin the longitudinal direction (Y(MD)) at 25° C. is at least 2.5 GPa. 2.A biaxially stretched polypropylene film comprising a polypropylenewhich consists of a polypropylene having a melt strength (MS) and a meltflow rate (MFR) measured at 230° C. that satisfies formula (2) below:log(MS)>−0.61 log(MFR)+0.52  (2) and a petroleum resin substantiallycontaining no polar-group and/or a terpene resin substantiallycontaining no polar-group that has compatibility with the polypropyleneand provides plasticity during stretching, wherein the Young's modulusin the longitudinal direction (Y(MD)) at 25° C. is at least 2.5 GPa. 3.The biaxially stretched polypropylene film according to claim 1 or 2,wherein the polypropylene has a meso pentad fraction (mmmm) in the rangeof 90 to 99.5%.
 4. The biaxially stretched polypropylene film accordingto claim 1 or 2, wherein the m value represented by the Young's modulusin the longitudinal direction (Y(MD)) and the Young's modulus in thetransverse direction (Y(TD))m=Y(MD)/(Y(MD)+Y(TD)) is in the range of 0.4 to 0.7 at 25° C.
 5. Thebiaxially stretched polypropylene film according to claim 1 or 2,wherein, in a 1-μm square area of a surface of the biaxially stretchedpolypropylene film, one side of the area being parallel to thelongitudinal direction, at least one longitudinal fibril having a widthof at least 40 nm and extending across two sides parallel to thetransverse direction is present.
 6. A biaxially stretched polypropylenefilm comprising a polypropylene which comprises a polypropylene having aTrouton ratio of at least 30 and a petroleum resin substantiallycontaining no polar-group and/or a terpane resin substantiallycontaining no polar-group that has compatibility with the polypropyleneand provides plasticity during stretching, wherein the Young's modulusin the longitudinal direction (Y(MD)) at 25° C. is at least 2.5 GPa. 7.A biaxially stretched polypropylene film comprising a poly-propylenewhich consists of a polypropylene having a Trouton ratio of at least 16and a petroleum resin substantially containing no polar-group and/or aterpane resin substantially containing no polar-group that hascompatibility with the polypropylene and provides plasticity duringstretching, wherein the Young's modulus in the longitudinal direction(Y(MD)) at 25° C. is at least 2.5 GPa.
 8. The biaxially stretchedpolypropylene film according to claim 6 or 7, wherein the polypropylenehas a meso pentad fraction (mmmm) in the range of 90 to 99.5%.
 9. Thebiaxially stretched polypropylene film according to claim 6 or 7,wherein the m value represented by the Young's modulus in thelongitudinal direction (Y(MD)) and the Young's modulus in the transversedirection (Y(TD))m=Y(MD)/(Y(MD))Y(TD) is in the range of 0.4 to 0.7 at 25° C.
 10. Thebiaxially stretched polypropylene film according to claim 6 or 7,wherein, in a 1-μm square area of a surface of the biaxially stretchedpolypropylene film, one side of the area being parallel to thelongitudinal direction, at least one longitudinal fibril having a widthof at least 40 nm and extending across two sides parallel to thetransverse direction is present.
 11. The biaxially stretchedpolypropylene film according to claim 10, wherein the formula betweenthe Young's modulus in the longitudinal direction (Y(MD)) at 25° C. andthe heat shrinking in the longitudinal direction (S(MD)) at 120° C. issatisfied:Y(MD)≧S(MD)−1.